I recently had a customer upgrade to their cluster to CUCM 10.5(1) as well as their IM&P servers to 10.5(1). They ran into an situation with the IM&P subscriber server that ended up requiring intervention from TAC to get running. (I also noticed a number of other customers having this exact same issue.)
The symptom is that after the IM&P subscriber upgrade completes, the administrator screen goes blank when trying to login and the sync service won’t start.
The issues is caused by a CUCM LDAP sync occurring while the IM&P servers are being upgraded. This causes all of the users assigned to subscriber IM&P servers to be unable to login.
If your server ends up in this condition, a call to TAC would be the first thing to do so that they can do a remote support session to fix the issue.
Avoiding the Problem in the First Place
Before performing a system upgrade of CUCM and IM&P, change the LDAP sync interval to a sufficiently long period to avoid having a sync occur during your upgrade window. I’d push it out o a week or so, but make sure it isn’t going to happen during your upgrade. This is the cause of the issues.
Upgrade CUCM and IM&P as normal
Change your LDAP sync interval back to previous values (many engineers set it to 24 hours).