Hi @SebastianT, I found that my system tells me step 4 is still running… searching that in Nextcloud forum helped.
As far as I see it I had an issue with the backup which shouldn’t as the USB drive is half full so enough space at least. After starting the cmd line with telnet to Synology NAS it worked out to stop maintenance mode, then running web interaface told me step 4 is still ongoing… since more than 24 hours? Ok looking for that immediately helped.
So I hope this helps others as well. Wasn’t to easy but also not very complicatged to start Telnet in Synology, and use standard Win 7 client and login as standard user and change do super user with sudo then php56 instead of only php and my -u (user parameter) should be http for us Syno guys.