From my GameLift web console:
everything was fine till 2021-03-04 20:32:50 UTC+0100 (I download all downloadable logs and they was fine), but the fleet stayed for about an hour in ACTIVATING state then went in ERROR state without the evidence of an error.
I connected in ssh to the created instance and from the logs I learned that GameLift neither tied to launch a server.
Please ignore the last error message: from the ssh connection I tried to launch the server by hands and it worked as expected (obviously untill it tried to connect to GameLift).
What should have been happened in that hour to avoid the fleet to go in ERROR state?
Fleet ID (to easly cut&paste it in case you need): fleet-f486d04a-e5c6-475c-8f44-d23c14747ed2