An issue does not get synchronized and appears in the troubleshooting section with the category 'User was not mapped' and the message, e.g. 'User at position -1 was not mapped to field 'Multi User Field' (customfield_10302)'. The part 'customfield_10302' identifies the internal id of the field which is affected.
You are using a correlation mapping for a (multi) user field but one user was not mapped properly. This means the user was not mapped on either the sender or receiver side. A position of "-1" indicates that the user was not added on the sender side. A position of "0" or greater indicates that a user was not mapped at the same position on the receiver side.
Check if you have added all users to the correlation mapping. The following steps should be done in order to resolve this problem:
- If necessary, change the user mapping settings in the synchronization configuration
- After fixing your configuration trigger a resync for the affected issues, e.g. using a JQL filter like "key in (ABC-1, ABC-2)"