Owncloud -> Nextcloud with imap backend fails

Hi,
I also just upgrdaded from OC 8.2.5 to NC .
To get the IMAP authentication working I had to enable it on the command line as it’s not shown in the web UI (?!)

No, it seems to be working find, but I see duplicated user accounts in the admintstration overview which worries me a bit.
Same username, but different fullname, group, quota, last login.

edit: Further investigation of this is discussed in another thread