This build works fine locally. After a lot of debugging attempts (it always shows "pending heartbeats" in the uploaded build but runs fine in LMA), I ended realizing that the process didn't even start inside the machine, after I managed to connect to the remote virtual machine, go inside the container trough docker exec, and test on it.
I tried running another instance of the process under strace both in localagent and the uploaded build. localagent runs fine but the uploaded build stops here:
As you can see everything goes wrong after a "operation not permitted" and this was the reason why the uploaded build never ever got to create a log file like it did in the LocalAgent container despite the process being running: the process got stuck here and went to sleep. At first I thought it may be the process crashing or taking too much CPU, but neither the server gets killed (a complete crash kills the server completely and you can't go inside it remotely), and neither CPU goes upwards of 0% nor the ram upwards of 200MB. CPU only gives a tiny "bip" when trying to launch as seen in VMetrics.
What can be causing this problem with permissions (or whatever its causing this operation not permitted) in the uploaded container but not while using the same image in the LocalMultiplayerAgent test? I connected both to the remote container and the local container trough the same SSH command to perform the testing.