Under Xojo 2017r3 Macintosh, I can set a breakpoint in some code in the action event of a module-resident, enabled, mode-multiple timer which has a 50ms period, but the breakpoint never fires. If I click the IDE Pause button while the app is running, though, I can see that this code is in fact executing and I can step through it, so the timer is definitely firing and the code where the breakpoint is set is executing. I’ve also verified that it’s firing by writing to System.Debuglog.
I’ve seen it also with some third-party plugin objects’ events, but in the instance above, it’s just a plain old Xojo timer.
I think that I’ve seen it only with objects contained in modules; breakpoints elsewhere work fine.
Sometimes the flaky breakpoint will fire once or twice and then stop. I quit and relaunched Xojo but no joy.