In general, while iterating over the timers returned via TImerService.getTimers(), any method invoked on the timer can throw an exception if the timer is canceled.
WRT, IdleThresholdTimerPassivationTestCase since the timer in question is a single action timer, its methods will always throw an exception after its timeout has elapsed.

https://ci.wildfly.org/buildConfiguration/WF_PullRequest_WindowsJdk17/535437