Client never initializes on .NET Framework 4.8 MVC Application

[rkajbaf-experientgroup]

Is this a support request?
No,

Describe the bug
Fails to ever initialize in a .NET Framework 4.8 Web Application on the latest version (8.0). Downgrading to 7.1 resolves the problem.

To reproduce
Try on a .NET Framework MVC Application. Client will never initialize.

Expected behavior
Should initialize.

Logs
If applicable, add any log output related to your problem.

SDK version
8.0

Language version, developer tools
.NET Framework v4.8

OS/platform
Windows

Additional context
Downgrading to 7.1 resolves the problem.

[tanderson-ld]

Hello @rkajbaf-experientgroup and thank you for your feedback. Are you able to collect any logs? Could you please provide a code snippet of your configuration and call to start the SDK? Thank you!

[tanderson-ld]

Another theory is that a cache or lockfile is holding a version of a library or dependency. Have you tried a clean build and/or do you use a package lockfile?

[pgeorge-costacoffee]

I am also having this problem; unrelated to the individual who posted this originally. I even opened a Stack Overflow post a couple months ago:

https://stackoverflow.com/questions/77869557/launchdarkly-example-doesnt-work-in-net-class-library-but-does-in-a-consoleapp

[pgeorge-costacoffee]

Here is the console output related to launch darkly:

'my.exe' (CLR v4.0.30319: my.exe): Loaded 'C:\my-project\bin\x64\buildconfig\LaunchDarkly.CommonSdk.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
'my.exe' (CLR v4.0.30319: my.exe): Loaded 'C:\my-project\bin\x64\buildconfig\LaunchDarkly.ServerSdk.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
'my.exe' (CLR v4.0.30319: my.exe): Loaded 'C:\my-project\bin\x64\buildconfig\LaunchDarkly.InternalSdk.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
'my.exe' (CLR v4.0.30319: my.exe): Loaded 'C:\my-project\bin\x64\buildconfig\LaunchDarkly.Logging.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
2024-04-12 15:45:06.506 -05:00 [LaunchDarkly.Sdk] INFO: Starting LaunchDarkly client 8.3.0
'my.exe' (CLR v4.0.30319: my.exe): Loaded 'C:\my-project\bin\x64\buildconfig\LaunchDarkly.EventSource.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
2024-04-12 15:45:06.630 -05:00 [LaunchDarkly.Sdk.DataSource] INFO: Connecting to LaunchDarkly stream
2024-04-12 15:45:06.643 -05:00 [LaunchDarkly.Sdk] INFO: Waiting up to 10000 milliseconds for LaunchDarkly client to start...
2024-04-12 15:45:06.929 -05:00 [LaunchDarkly.Sdk.DataSource] ERROR: Unexpected error in stream processing: System.IO.FileLoadException: Could not load file or assembly 'System.Runtime.CompilerServices.Unsafe, Version=4.0.4.1, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
2024-04-12 15:45:07.455 -05:00 [LaunchDarkly.Sdk.DataSource] INFO: Waiting 853 milliseconds before reconnecting...
2024-04-12 15:45:08.462 -05:00 [LaunchDarkly.Sdk.DataSource] ERROR: Unexpected error in stream processing: System.IO.FileLoadException: Could not load file or assembly 'System.Runtime.CompilerServices.Unsafe, Version=4.0.4.1, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
2024-04-12 15:45:08.979 -05:00 [LaunchDarkly.Sdk.DataSource] INFO: Waiting 1064 milliseconds before reconnecting...
2024-04-12 15:45:10.199 -05:00 [LaunchDarkly.Sdk.DataSource] ERROR: Unexpected error in stream processing: System.IO.FileLoadException: Could not load file or assembly 'System.Runtime.CompilerServices.Unsafe, Version=4.0.4.1, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
2024-04-12 15:45:10.715 -05:00 [LaunchDarkly.Sdk.DataSource] INFO: Waiting 2966 milliseconds before reconnecting...
2024-04-12 15:45:13.829 -05:00 [LaunchDarkly.Sdk.DataSource] ERROR: Unexpected error in stream processing: System.IO.FileLoadException: Could not load file or assembly 'System.Runtime.CompilerServices.Unsafe, Version=4.0.4.1, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
2024-04-12 15:45:13.830 -05:00 [LaunchDarkly.Sdk.DataSource] INFO: Waiting 5497 milliseconds before reconnecting...
2024-04-12 15:45:16.657 -05:00 [LaunchDarkly.Sdk] WARN: Timeout encountered waiting for LaunchDarkly client initialization
2024-04-12 15:45:26.143 -05:00 [LaunchDarkly.Sdk.Evaluation] WARN: Flag evaluation before client initialized; data store unavailable, returning default value
2024-04-12 15:45:26.226 -05:00 [LaunchDarkly.Sdk.DataSource] ERROR: Unexpected error in stream processing: System.IO.FileLoadException: Could not load file or assembly 'System.Runtime.CompilerServices.Unsafe, Version=4.0.4.1, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
2024-04-12 15:45:26.745 -05:00 [LaunchDarkly.Sdk.DataSource] INFO: Waiting 10881 milliseconds before reconnecting...

[pgeorge-costacoffee]

Based on the output, above dug in some more. Was able to resolve it following the steps here:

https://stackoverflow.com/a/78331233/16276333

[tanderson-ld]

Tried to reproduce this issue by creating a .NET Framework 4.8 class library and then using that in a console application. It appears to have worked fine, so at the moment we cannot reproduce this.

[JoshuaMS7]

It caused another issue for "Failed to initialize LaunchDarkly connection.|System.IO.FileLoadException: Could not load file or assembly 'LaunchDarkly.Logging, Version=2.0.0.0, Culture=neutral, PublicKeyToken=d9182e4b0afd33e7' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
File name: 'LaunchDarkly.Logging, Version=2.0.0.0, Culture=neutral, PublicKeyToken=d9182e4b0afd33e7" after downgraded sdk to v7.1. Any other option except to add bindingRedirect into config since we need to apply into many services and websites? Is adding into machine config a bad practice and considered as complete hack? Please advise. Thanks.

[jsonbailey]

@JoshuaMS7 I can recreate the error you are experiencing and am looking at it today.

[JoshuaMS7]

Another error found is that couldn't load launchdarkly.commonsdk v7.0.0 when initializing connection after upgraded the launchdarkly serversdk to v8.92 to fix my performance issue but actually it's implicit reference to launchdarkly.commonsdk v7.0.1 and no way to be downgraded. Think this is an error from launchdarkly for serversdk v8.92?

[jsonbailey]

Yes, there is currently a mismatch in the common.sdk package version numbers. I have an update in review and I'll let you know when a new version is released with the fix. Long term we plan to make some changes to help prevent the need for binding redirects but there are a few other items ahead of that work.

[JoshuaMS7]

After upgraded serversdk to v8.10.0 and it caused error for "System.IO.FileLoadException: Could not load file or assembly 'LaunchDarkly.CommonSdk, Version=7.1.0.0, Culture=neutral, ..." instead of Version=7.0.0 in this time. I'm trying to apply transitive reference to LaunchDarkly.CommonSdk v7.1.0.0 and it caused "System.IO.FileLoadException: Could not load file or assembly 'LaunchDarkly.ServerSdk, Version=8.10.0.0" error. Can help to check?

[JoshuaMS7]

Yeah being solved the load assembly issue but it seems caused the error below.

LaunchDarkly: 2025-07-14 12:20:31.812 +10:00 [LaunchDarkly.Sdk.DataSource] DEBUG: Making GET request to EventSource URI https://stream.launchdarkly.com/all
2025-07-14 12:20:31.8449|INFO | 129|-LaunchDarkly: 2025-07-14 12:20:31.844 +10:00 [LaunchDarkly.Sdk.DataSource] DEBUG: Response status: 200
2025-07-14 12:20:31.8449|INFO | 129|-LaunchDarkly: 2025-07-14 12:20:31.844 +10:00 [LaunchDarkly.Sdk.DataSource] DEBUG: EventSource Opened
2025-07-14 12:20:31.8449|INFO | 129|-LaunchDarkly: 2025-07-14 12:20:31.844 +10:00 [LaunchDarkly.Sdk.DataSource] DEBUG: Reading UTF-8 stream without string conversion
2025-07-14 12:20:31.8449|INFO | 129|-LaunchDarkly: 2025-07-14 12:20:31.853 +10:00 [LaunchDarkly.Sdk.DataSource] DEBUG: Received event "put"
2025-07-14 12:20:31.8449|INFO | 129|-LaunchDarkly: 2025-07-14 12:20:31.853 +10:00 [LaunchDarkly.Sdk.DataSource] ERROR: Unexpected error in stream processing: System.IO.FileLoadException: Could not load file or assembly 'System.Memory, Version=4.0.1.1, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
2025-07-14 12:20:31.8449|INFO | 129|-LaunchDarkly: 2025-07-14 12:20:31.853 +10:00 [LaunchDarkly.Sdk.DataSource] DEBUG: at LaunchDarkly.Sdk.Server.Internal.DataSources.StreamProcessorEvents.ParsePutData(Byte[] json)
at LaunchDarkly.Sdk.Server.Internal.DataSources.StreamingDataSource.HandleMessage(String messageType, Byte[] messageData)
at LaunchDarkly.Sdk.Server.Internal.DataSources.StreamingDataSource.OnMessage(Object sender, MessageReceivedEventArgs e)

Finally getting the error below.
2025-07-14 12:21:53.7767|INFO | 129|-LaunchDarkly: 2025-07-14 12:21:53.776 +10:00 [LaunchDarkly.Sdk.DataSource] INFO: Waiting 28001 milliseconds before reconnecting...

May i know is any idea since it was only happen in website app (IIS based) instead of window app?