Some AD users not able to log in

We are using Openfire 3.6.4 and Spark 2.5.8 and it’s integrated with our Active directory. It is working great for everyone except for a handful of people. They are in the same security group and OU as everyone else, but when they try to log in, it comes back with invalid username and password. Here is what we have tried so far. Restarted the openfire service, removed the users from the security group, and added them back in. Newly created users are able to log right in, minutes after their accounts are created. Does openfire cache the user accounts and passwords? If so, how often does it check for changes? We do have a 60 password change policy. I guess I need more ideas to try. Oh, there’s nothing unusual about the usernames, standard first initial last name (ex. jsmith). Thanks in advance for your help.

So far , the only work-around that we have found is to create another Active Directory user account with the same First/Lastname, but a different username/password. This would still show the persons full name under the contact list. Explained to the user that this is a spark username and password only.