@jubamo

tried your suggestion; with no effect; Flaps starts the flashing routine with BLOCK ERASING.

the display shows:

Erasing block: 1 (addr = 1fc0000)... done
Erasing block: 2 (addr = 1fc0400)...

and nothing more !!!

That's the same which I know from earlier versions of WRT.

So might be something else, maybe hardware dependand.

If you want a photo from pcb in high res, please let me know