Hello @AroWhite
the first M5Stack device, M5Stack Basic, came w/o PSRAM, so using GPIO16 and GPIO17 for UART was an ok, albeit unlucky, choice.
Note: most functions (I2C, UART, etc.) can be assigned to almost any GPIOs. Unfortunately PSRAM is an exception and requires GPIO16 and GPIO17 to be used.
BTW: I think you should be able to use Groove port B as UART (GPIO36 and GPIO26).
Thanks
Felix