I made the conversion on Garniak.pl on my 255w. All good is only the software 3.21 and in vain upgrade to Express 4.20 only after the old 3.21 remains / professionally unmounted.
It's just that the date isn't right.
I read there that after loading the 4.20 software it will only reach the Garmin logo and will become a door prop. If my 255w does it with what you wrote, don't I have to worry about it?