Thanks for the support!
I will contact  HagssFIN too.

More progress, one of the boards was set back to factory defaults successfully, all others are reacting inadequate.
The one with 10 seconds online behaviour - after putting new fans started to perform normal, no red blinking anymore etc. Now the next drama, 0 hashboards, will soft this out slowly.
Tried to update to the last firmware, failed:  A1047-A1026_20033101_daa810f_57f076c.aup