Hi, short feedback: here, we had exact the same problem:
LDAP Error: Undefined attribute type: kopanoMrAcceptRecurring: attribute type undefined
It was solved by the comment from @damrose
Please update the packages on the DC Master and all DC Backups via
univention-app install --only-master-packages --do-not-install-master-packages-remotely kopano-core
Then, run the join scripts again.
Logs from that App update would be interesting.
From the server where the update was started (probably your DC master) and the server kopano is installed
Running 70kopano4ucs.inst failed (exitcode: 3)