Message bus is no longer functioning correctly

I’m seeing this message show up in the logs after a recent update

Global messages on 379645 timed out, message bus is no longer functioning correctly

Backtrace

message_bus-4.2.0/lib/message_bus.rb:748:in `block in new_subscriber_thread'
message_bus-4.2.0/lib/message_bus/timer_thread.rb:117:in `do_work'
message_bus-4.2.0/lib/message_bus/timer_thread.rb:95:in `block (2 levels) in queue'

What does it mean?

Version
2.9.0.beta8
(d5dc4ca0e9)