I had a problem like this. It was a bug in my own code. I did not append the actions to the queue using the java action. The queued Objects have been there but they have only been executed after a restart. Calling the appendnewactiontoqueue java action after creating the QueuedAction solved the problem.
But if it is only happening sometimes and on existing code, it might be something else.
For me the queued jobs had status unqueued when they stalled so it might not be the same problem as you have had. Reinitialized did not do us any good either
I have tried the solution in these threads, and so far it seems to not stall:
https://forum.mendix.com/link/questions/88867
https://forum.mendix.com/link/questions/88368
Today again a problem where the que stopped running.
It's getting annoying.
The implemented solution to restart the processque (executing BeforeShutdown_Shutdownqueues and Afterstartup_InitializeQueue) had no result.
I had to restart the mendixapp to get it going again.
After restarting all queues work fine.