In your OpenVPN AS management GUI, go to
Status > Log Reports and see what type of errors are showing up.
It could be that for whatever reason one of your clients is connecting twice and using up your free licenses.
When I am testing connections I usually look at the
Current Users section when connecting to see what's happening and troubleshoot.
You can also run the following at the command line to look for clues:
tail /var/log/openvpnas.log