Would be more easier for them to fix this problem if the game could log the multiplayer status while playing. Either in a file on the PC you later send here, or on Galaxy sending directly to them. The multiplayer itself working, but the performance is nowhere near to expected, not even close to enjoyable. This problem is more troublesome than a not-even-working multiplayer because much harder to track the process and catch where it mess up.
But no one would like if GOG watch the gaming I'm sure. I never liked these tracking clients, but have to accept the fact that would at least gives a hope for a fix. And before anyone going into a false alarm, GOG doesn't do this. I said it as an example way to search for the problem.