I think I found out what the issue is I also had noticed the difference is that clicking on Login as Owner for the users with an error goes to https://xxxxx/admin/client/548/login for imported users from Blesta and the ones created via WHMCS work go to https://xxxxx/clientarea.php.
I looked at the Table: tblusers and noticed the password are empty. I created a password for that user then tried to Login as Owner and it worked!
Looks like passwords will need to be set manually for the ones migrated from a different platform. Hope this helps others with this issue.