Some users unable to login via OpenLDAP Undefined method 'provider' for nil:nilclass

Some of our users are unable to login to Gitlab using LDAP while others are. When researching the issue, we found a couple of other threads submitted by others that were using 7.x Gitlab and they said it was fixed when upgrading to the next higher version. We’re currently at version 8.3.2. As others have said, we can go into the Users’ settings and change their email address to our own and they’re able to login, but this is obviously not ideal as we’d also like to be able to use Gitlab at the same time. Please let me know what info I can provide to get this issue resolved. This is a recent production server that’s on a virtual machine with the following hardware specs:
4 processors (2 cores, 2 sockets), 16GB RAM, 112GB HDD, CentOS 6.7

Error some users see while attempting to login:
"Could not authenticate you from Ldapmain because “Undefined method ‘provider’ for nil:nilclass” ".

cc @dblessing