Betterbird: Send Later hangs in main loop delivering message

[jikamens]

With Betterbird 115.10.0-bb27 on Linux, if I schedule a message, then Send Later delivers the scheduled message but then stops at that point and no further messages are delivered until I restart Betterbird or deactivate and reactivate the add-on. Something inside the main loop after message delivery appears to be hanging. Need to investigate further.