Hello and welcome to the forum,
searching for the error message I find that it's an elementary Python exception which is likely to occur where some code isn't properly prepared to deal with some kind of nested multivalue data items.
Unfortunately, looking at the source code, I can't easily dig to the point where the exception is really thrown, so I can't see which data item triggers the exception. At one point, it ends at a wrapper code which doesn't reveal what was wrapped here. (at least to me; perhaps the developers can see better?)
I would try to examine the data of the given user, just to find the difference to the other users.
[li] on the DC master, the command
always dumps the full LDAP directory. Pipe the output into a file and try to compare user data field-by-field.
[li] Increase the log level of the UDM CLI
try to trigger the error again by retrieving the given user
and examine the file
for errors, hints or traces leading to the cause. (and don't forget to set the debug level back to its previous value)[/li][/ul]
User management in UCS was recently enhanced by introduction of a new DC mode where the UCS directory is synchronized with a "real" AD domain. Perhaps this change introduced some marginal bugs, and you just found one. If your findings reveal which data item causes the error it can help the developers fix it.