PSA: Signal deprecated another group-related API, which means that group updates and joins will not work. Receiving messages will still work correctly. Gabriel is patching this up, I’ll try to integrate this ASAP in Whisperfish!
Concretely, if you are added to a group, you will see incoming messages, but you will not be able to send any. If a new member joins, they will not receive your messages. You can still use Signal Desktop in the mean time.