I'm not seeing an obvious cause for that; it should process moderator roles per user. Only potential situation I could see is if multiple users that were both moderators were merged together -- that's a situation that's fairly difficult to handle here. (Though there may actually be code to handle that.)
Any idea if there is a merged user involved here? If you refresh, does it happen again?
Did get it to import, like you say it was my account that caused the problem. I had selected the second option when merging moderators and it failed, selected the first option the second time and it went ahead.