I have tested the changes from JBPM-8485, with the following results:

(1) @[PT5S]

==> OK: Notification emitted once after 5s:

08:52:35,296 INFO [stdout] (default task-1) Process created
08:52:36,471 INFO [EmailNotificationListener] (EJB timer-thread-pool - 1) Missing mail session or userinfo - skipping email notification listener processing
(2) @[R3/PT5S]

==> NOT OK: Notification emitted at defined intervals, but the timers seem to get duplicated on each rescheduling:

09:09:50,439 INFO [stdout] (default task-1) Process created
09:09:55,514 INFO [EmailNotificationListener] (EJB timer-thread-pool - 7) Missing mail session or userinfo - skipping email notification listener processing
09:10:00,062 INFO [EmailNotificationListener] (EJB timer-thread-pool - 8) Missing mail session or userinfo - skipping email notification listener processing
09:10:00,505 INFO [EmailNotificationListener] (EJB timer-thread-pool - 9) Missing mail session or userinfo - skipping email notification listener processing
09:10:05,055 INFO [EmailNotificationListener] (EJB timer-thread-pool - 11) Missing mail session or userinfo - skipping email notification listener processing
09:10:05,088 INFO [EmailNotificationListener] (EJB timer-thread-pool - 10) Missing mail session or userinfo - skipping email notification listener processing
09:10:05,114 INFO [EmailNotificationListener] (EJB timer-thread-pool - 12) Missing mail session or userinfo - skipping email notification listener processing
09:10:05,512 INFO [EmailNotificationListener] (EJB timer-thread-pool - 13) Missing mail session or userinfo - skipping email notification listener processing
(3) @[3s]

==> NOT OK: Notification emitted only once after the defined interval:

09:14:12,753 INFO [stdout] (default task-1) Process created
09:14:15,816 INFO [EmailNotificationListener] (EJB timer-thread-pool - 15) Missing mail session or userinfo - skipping email notification listener processing
This is a regression from previous versions, where the notification was emitted repeatedly in the defined interval.