Mentor Account Do not Exist on Steplab
Check the Sync logs on Steplab. On Steplab , go to Manage --> Admin tools--> Teach First Sync Logs --> Search for the trainee with either name , email or SF id.
If a trainee has sync error on steplab which is pointing to duplicate mentors like the one in below screenshot:
Then this is an issue of Trainee - mentor duplicate relationship being created on MYTF.
The issue occurs looks when there existed another duplicate relationship page which got deleted later , but before its deletion it got sent to MYTF , so it ended up creating duplicate relationship on MYTF . Please raise this issue to L3 (Sakshi Prabhakar) where she will be able to delete the duplicates on MYTF ,for above error to not come up on Steplab.