message was not bridged - mautrix signal

[neonblind]

Describe the bug
Sending a message to a Signal contact via mautrix-signal bridge I got the error:
Your message was not bridged: failed to get group session: group session has been withheld: com.beeper.redacted (Session redacted: expired).

To Reproduce
Steps to reproduce the behavior:

1. start chat with signal contact
2. after some time this error happens
3. a /discardsession fixes it temporary

Expected behavior
message should be sent

Smartphone (please complete the following information):

• Device: Sony X Compact
• OS: Android 8.0 (latest stock firmware)

but happens with all my devices

Additional context

• App version: 1.6.22.sc81
• Store: Google Play
• Homeserver: selfhosted (Synapse 1.116.0)
• Related labs settings: none, don't know, only timeline settings active
• Logs have been submitted using the app's built-in bug report (/"rageshake") mechanism: no

Upstream relevance

• Does this issue exist in Element Android? no