Replied to the thread OMV 3.x resolved Can't reach WebGUI after update 3.x. SSH is working.Post
Reacted with to mjnaylor8’s post in the thread OMV 3.x resolved Can't reach WebGUI after update 3.x. SSH is working.Reaction (Post)I had a similar problem moving from 2.x to 4.x on logon.
I executed the commands
systemctl unmask openmediavault-engined
systemctl enable openmediavault-engined
systemctl restart openmediavault-engined
and all was OK