Why Timer hangs?

I have an engine embedded in Spring Boot. I’ve been seeing sometimes a Timer is hanging forever. I queried DB and all the 3 timers should have already triggered but they were not triggered.

Note, for testing purpose, I’ve set all 3 timers as PT0M.
Note, in application.properties, I’ve set
camunda.bpm.job-execution.enabled=true
camunda.bpm.job-execution.deployment-aware=true

These Timer are all hanging forever. What could be the cause?

image

@Niall, could you advise?