A specific Signal user isn't receiving my messages bridged from Matrix anymore

[bnjbvr]

I've been using the signal bridge for a while and I'm quite happy with it, thanks!

For a week or so (didn't update any software in the stack during this time), there's one specific Signal user who doesn't receive my messages. They claim they get errors from Signal, telling that some message couldn't be received. That's only for one of their devices, as they confirm they see my messages on their other devices. It looks like a session between the server-side puppet and this specific device of theirs is somewhat in a broken state. I can see my own messages in Matrix and in my own Signal just fine, so it's not in a globally broken state.

I've been using the following:

• synapse 1.134
• the signal bridge uses encryption. It's running in a docker instance, I've pulled the latest image as of a few minutes ago, its sha is thus sha256:6f376a6e58b5586fa3899b73c7d340b7cc30c0d460836e46e752f35cdcfe6e09.

Logs showed this error multiple times, not sure it's related (I'd imagine it would cause UTDs on my side):

signal-1  | 2025-07-24T07:21:26.92Z ERR Decryption error with known sender error="failed to decrypt unidentified sender envelope: unsupported plaintext sealed sender messag
e" action="start receive loops" client_ts=1753341686052 content_hint=IMPLICIT envelope_timestamp=1753341686052 handler="incoming request handler" incoming_request_id=374603etc
 login_id=d022192a-4c3b-4bc2-etc path=/api/v1/message sender=5425ad04-etc server_timestamp=1753341686870 server_ts=175334
1686870 urgent=false user_mxid=@bnjbvr:example.org username=something-that-resembles-a-uuid.3 verb=PUT websocket_type=authed

I've tried the following, with no success:

• request another megolm session for the room
• updating the bridge to the latest version
• updating synapse and restarting the entire matrix stack

Please let me know if I can provide more debug information, one way or another.

[bnjbvr]

Another user has started to not receive my messages either, on one of their devices (the others work just fine). So it seems another session is broken, somehow…

In the logs, I'm seeing this:

signal-1 | 2025-08-31T15:27:26.312Z DBG Got error while encrypting event for room, sharing group session and trying again... error="session has expired" component=crypto room_id=!abcde:example.org

Then what seems to be a new session being created. But the person on the other side seems to say they haven't received the message on their Signal mobile app.

[robotfishe]

I am seeing this as well. A specific person is unable to see my messages, both private messages and in a group chat. The error message they get just says "a message from [my name] couldn't be delivered".

[Zepmann]

I can confirm this.

Logging from mautrix-signal when this occurs:

Oct 24 09:43:16 matrix matrix-mautrix-signal[3571]: 2025-10-24T07:43:16.635Z ERR Decryption error with known sender error="failed to decrypt unidentified sender envelope: unsupported plaintext sealed sender message" action="start receive loops" client_ts=1761291774201 content_hint=DEFAULT envelope_timestamp=1761291774201 handler="incoming request handler" incoming_request_id=(...) login_id=(...) path=/api/v1/message sender=(...) server_timestamp=1761291796582 server_ts=1761291796582 urgent=false user_mxid=(...) username=(...) verb=PUT websocket_type=authed
Oct 24 09:43:16 matrix matrix-mautrix-signal[3571]: 2025-10-24T07:43:16.776Z ERR Decryption error with known sender error="failed to decrypt unidentified sender envelope: failed to decrypt ciphertext message: 30: invalid Whisper message: decryption failed" action="start receive loops" client_ts=1761291795470 content_hint=RESENDABLE envelope_timestamp=1761291795470 handler="incoming request handler" incoming_request_id=(...) login_id=(...) path=/api/v1/message sender=(...) server_timestamp=1761291796732 server_ts=1761291796732 urgent=false user_mxid=(...) username=(...) verb=PUT websocket_type=authed

The recipient reports that messages are missed on the Signal desktop client. They are readable on the smartphone running Signal.