After upgrade firmware 6.40.5, Can't change admin's group to full

The solution is to use the winbox email tool bug, which I had reported to the support. I don’t want to share the details here, sorry.

I think we got hit with this also - several routers not responding to the administrator password although we are scrupulous about replacing ‘admin’ and using a secure password on every device.
Router is not responding to hard reset also so I am suspicious reformat hold period is changed also

How is it possible to see this script if router access is denied?

Well if you got lucky and there was no rx-bits-per-second on any of interfaces when script was executed, then reformat-hold-button=299-5 and reformat-hold-button-max=300-5.

i’ve held the reformat button down for over 4 mins but no good