Hi Thibaud
Error message "Calculated UME LDAP id is null", Is it occurring for only one user ?
It seems that the user does not exist but its reference is still present in the LDAP. I would suggest you run UME Consistency Check tool and remove all the objects which are found as inconsistent.
Please refer Note # 1016283 - UME Consistency Check Tool
Do not forget to take backup of the userstore before performing repair operation.
Also refer to the Note # 2195487 - Error While Populating "USER.CORP_LDAP
Let us know if this resolves your problem.
Regards
Santarshi Samanta
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