Hi MicahBennard-1617,
Does this issue happen on the only user?
Do you try to log in other machines and check the results?
The contact lists are saved in RTC database. You can run the following command to test the connectivity for RTC database:
Test-CsDatabase -DatabaseType "Registrar" -SqlServerFqdn "sql.doamin.com" -SqlInstanceName "default"
If the result is false, it recommends you check if there is any error event in Skype for Business server.
If the result is true, check if there is any update on the OS.
In addition, try to disable and reenable the user account in Skype for Business front-end server.