Builtin Icons dissappear when activating SPFx package (SPSE onprem, no internet)

[ruudsolidnl]

Target SharePoint environment

SharePoint SE Onprem without internet connection

What SharePoint development model, framework, SDK or API is this about?

💥 SharePoint Framework 1.4.1

Developer environment

VSCode, default SPFx toolchain for 1.4.1

What browser(s) / client(s) have you tested

• 💥 Internet Explorer
• 💥 Microsoft Edge
• 💥 Google Chrome
• 💥 FireFox
• 💥 Safari
• mobile (iOS/iPadOS)
• mobile (Android)
• not applicable
• other (enter in the "Additional environment details" area below)

Additional environment details

• Edge latest
• SPFx 1.4.1
• Node 8.17.0

Describe the bug / error

When my application customizer is activated in a SE site, some out of the box icons dissappear. For example the Site usage icon on the viewlsts.aspx page. This happens because the page tries to load woff files from a cdn (http://static2.sharepointonline.com/files/fabric/assets/…) which fails because the farm does not have internet access. On another farm without internet access it does work.

The calls to the internet CDN are made from within the file "[server name]/_layouts/15/next/spclient/0.legacy-third-party-fabric-core.js?uniqueId=1PbbH0".

The other farm without the issue loads in the same file with a slightly different name: 69.legacy-third-party-fabric-core.js, and uses the following notation to refer to URLs: t(e(17)).

Since these files are hosted in the layouts folder in the farm I assume these are not added or modified by installing SPFx package in the appcatalog site. The only real difference between the farms is that the farm with correct behaviour is on CU May 2025, the other farm on CU April 2025. However, the file in the layouts folder is not replaced last months and also not in the list of the CU files.

The farm with the error is a new install, the correct working farm is a in place upgrade from a SP2019 farm (single server).

So the big question here is when is this file provisioned and which component in the SPFx package is referring to this file and how can we solve this?

Steps to reproduce

1. create a SPFx 1.4.1. package (app customizer, SP2019 and upwards, incl online, no tenant wide allowed)
2. install on a new teamsite (modern) in a SPSE farm without internet connection
3. open the site, open the dev console
4. you will see several calls to the CDN (URLS with static2 in it); these are called from within the file with name "[some number].legacy-third-party-fabric-core.js". In this file you will see the hardcoded URLs.

Expected behavior

I expect the farm to return the correct js file (0.legacy-third-party-fabric-core.js) with the correct URLs in there and not referring to an online CDN.

[Ashlesha-MSFT]

Hello @ruudsolidnl,
Thank you for bringing this issue to our attention. We will look into it and get back to you shortly.

[andrewconnell]

@StfBauer do you have any insights on this? I know it's an old SPFx install due to SPSE, but you've spent a lot more time on the nuances with Fabric/Fluent UI and thought of you first before I dig deeper...

[Amey-MSFT]

Hello @ruudsolidnl,
We were able to reproduce the issue, and we are investigating it. We have logged this as a bug, and our engineering team will look into it.
Thank you!