Random computers connected but not to domain

I have an issue where a random user will log in, and not be connected to the network. Checking the switch, i see they are connected. But on the WIN 10 computer the network is not seen.

I have:

1. Cleared the MAC from the switch and shut/no shut
2. Uninstalled NIC and driver

3. Used a MAC spoofer that gets it on the network.

   1. Reverted back to original MAC and loses connection again

4. Checked ARP tables and seem ok, haven't tried flushing the table though

5. AV/FW on/off

6. DNS is fine, oddly doing an ipconfig shows me the correct IP

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Any thoughts would be most welcome.