Arduino for STM32

I can't debug - because: I cant print anything betond 64 characters!!! That's how this started....BUT I just found it only happens in startup. If startup prints nothing at all, then all my debug messages now come pouring out: CONNECT as nucleo-f429zi FH=30000 ----> SEND CONNECT 79 bytes on wire <---...

Full sketch use ther external libraries, so not practical to post - I have narrrowed it down to the "hang" after it outputs 64 characters...

What's up with Serial.print on NUCLEO-F429ZI ? Trying to put some diagnostics in code...90% of my Serial.print statements cause the MCU to hang. In one place, Serial.printf("012\n"); works fine...replace with Serial.printf("0123\n"); MCU hangs Arduino 1.8.13 STM32 Core 1.9.0 Boar...