Thanks for the suggestion, but I gave up on it because it wasn't going to be my long term solution anyway.  I assigned the output to a serial port on the dev kit instead of the ITM output and haven't had any problems since.

I'm having the same problem with an STM32H745 Discovery board.  It will print to the data console for about 15 to 20 seconds and then I have to terminate the debug session and restart it before it will work again.  When I step through the _write() fu...