whichObject error

A hard crash when the Windows app is closed:

Runtime error
Failure Condition: whichObject

What can I be looking for to trap and correct whatever is causing this?

The same is happening here.

Any hint from Xojo due this seems an uncaught exception?

If memory serves , after I did some refactoring, I killed off all timers manually before I allowed the app to consider closing.

What do you mean with “killed”?
I have a timer but I’m sure was not running (ModeOff)

more or less that.

autotimer.Mode = timer.ModeOff
autotimer.enabled = false

on the window cancel close event

I remember seeing this a long time ago. In my case I was closing things down out of order and wound up breaking a dependency. In my case I think I had a web query in progress in a thread when I shut down the app without waiting for the query to complete and cleanly shutting the thread down.

Perhaps you have initiated something that requires responding but have closed down the caller so the response doesn’t know where to go.

This problem I never before, it started when compiling with 2018r2.

I will check my programs, but this is something it should not happen. Must be a Xojo bug.