Well, that is embarrassing.
I increased it to 2048, and yes it did work.
The serial prints - when present work - I usually open a Putty window.
I guess the ESP32 must need a lot more stack space to save its registers etc. It is a little weird, as on another project using the Portenta H7 (STM32H747) and MBed, I have some tasks that run with a stack size of only 256 bytes, and use only 120 bytes of them when using the runtime monitor.
Thanks for the Debug delay idea - that should be useful in the future.