If you think you have all necessary RDS configurations, licenses (CALs) etc in place, the possibility is, the issue might be related to a bug on Remote Desktop Session Host (RDSH) where it will not look to the Remote Desktop Services Licensing Server for CALs when the grace period ends.
Just for the fact, you can still connect to the computer reporting error through admin session, mstsc /admin
The solution to fix this error is to delete a registry key related to Grace Period.
Open registry editor (regedit) and go to ComputerHKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlTerminal ServerRCMGracePeriod
Delete GracePeriod key (folder).
Restart the server.
Note: remember you might have to repeat this every 120 days. Also Microsoft has released below hotfix for the same issue, shout out in comments if this works for you.
If for some reason you don’t need more than 2 remote sessions at one point of time, you can remove the Remote Desktop Services role. Windows by default allows 2 RDP sessions to the host machine that doesn’t require licensing server.