With version of Avalanche are you using? MC or SE? I had the samething, only with AP management (Avalanche MC). This was the solution:
When you add new licenses, you add them to the eServer. The eServer send the license to the dServer, when a device request a license.
What you can try. Stop the Wavelink Services and rename Wavelink.lic in "C:\Program Files\Wavelink\Avalanche\Service\MAIN.PRF" to Wavelink.lic.OLD and restart the Wavelink Services.
When all services are running, connect a Mobile Unit to Avalanche.
If the above doesn't work, you can try to remove the devices licenses from Avalanche and add them again.
Hope it helps
The version is MC 5.3.1 only using the D-server.
Thanks for the advice, restarting nad renaming the Wavelink.lic file didn't fix it.
After that i deleted all the licenses and re-entered them.
And a few minutes later all 18 units came back online and licensed .
Still doesn't explain why this happens after a server restart. Or why the uptime jumps to 287 days after that.
But i'm happy that the units are back.
Thank you very much.