Do not just restart the service. Do this exact sequence:
If VPN or unreliable Wi-Fi is the cause:
If you have tried all the above and error 2100 hot persists, escalate to Autodesk directly. Before contacting them, gather:
Autodesk support may need to re-host your license file or provide a hotfix for known bugs related to specific product versions (e.g., Revit 2022.1 had a known 2100 hot issue with multi-user environments).