Shit sticks. You’re spot on, I do recall reading that exact advice somewhere, then I promptly forgot it.
And now you mention it I remember discovering printing to serial doesn’t work in an interrupt handler. Something about reentrant interrupts and most likely getting such in a loop, sounds familiar.
I’ll give the serial print another go, the trace output gives me a bit of data overload sometimes.
I’ll let you know the outcome. Thanks for the advice.