Activate SSH
Connect via SSH with either
ssh root@IP
or
ssh admin@IP and sudo su
Change VERSION file as needed.
vi /etc.defaults/VERSION
Change:
6.0to5.06to57274or similair to5434Close editor withESC :wq ENTER
Login at Diskstation and do a manual update to a 5.x version. Restart Diskstation and do a Factory reset.
Have fun with your reverted and stable Diskstation! :)