Unexpected debugger breaks in uVision

I'm debugging a STM32F4 (custom board) with ST-LINK2 white dongle.
Everything looks good, but after some time running, the debugger unexpectedly stops as if it hits a breakpoint.
It does not look like exception. No breakpoints are set, and no breaks in the code.
ITM trace is used for debug prints. There are only few prints periodically, not a lot.

When I continue, it often stops again immediately, 1-2 times. After few minutes, another unexplained stop.

No message or popup shows up. Spooky!
Tried to reset the target, kill all breakpoints.
The chip is cold.

Please suggest how to avoid this. I need the program running!

MDK 5.26.2 on Win10.

Thanks,
Pavel A.