Autodesk licensing uses the ports 2080 and 27000-27009, so check that your firewall does not block these ports. Check the firewalls both on the workstations and on the license server.
If 2080 is blocked, you’ll see this error in the FLEXLM_DIAGNOSTICS output:
FLEXnet Licensing error:-15,570. System Error: 10035 “WinSock: Operation would block”