Zoom - import registrants by CSV and participants had to re-register to join meeting

Hello, 

I did a bulk import from CSV for participants of a scheduled Zoom meeting so participants didn't need to register themselves. When we held the actual meeting everyone was prompted to re-register in the meeting and some stuck in the dreaded registration loop though I re-sent the proper link to them. Is there some setting I may have missed when trying to do the registration import?