This has been an issue for me recently, I was trying to host a Left 4 Block zombie game mode, nothing fancy at all, just a default city with some creepy music and guns. At first I hosted a public sever and people kept leaving and re-joining because they say it is lagging. This happened with a couple people and they both started leaving and joining again at the same time and I got a windows error from steam about blockland failing or something, I could not read the whole message because it was gone and the game crashed.
Also, at a random time when I try to type something in the chat and when I hit ENTER it will not post what i typed, like the chat is frozen. I try to hit the windows button to the home screen and go back into the game but it crashes without warning as if i exited the game. I am using steam to run the game ever since I got the new computer. I used to just have the game separate from steam with my old pc.
I do not know if this helps but at the same time It crashed and I hit the windows button, my friend placed a TF2 style sentry as it crashed, but there was no sentry when It crashed any other time. At this point the sever was private and it was just me and my friend playing, nobody else. I had an excellent internet connection and a beefy computer so performance would not be the issue.
I do not know if I have an outdated Left for block or what, I have a lot of custom add-ons my friend made but I always used them before without issue, maybe because I am running the game from steam? This was my first time hosting since the new pc and I do not have this issue on single player. I am running RTB and blockland glass but the RTB chat has not been connecting since the other day. There was about 10k bricks on the sever, maybe 20 zombies, 5 vehicles, 7 music bricks playing a loop. My buddy was getting poor performance but he had a really crappy laptop to play it on so idk what the issue could be.
I could really use a hand here guys any help would be greatly appreciated and if you need any other information I can try to get it if it helps.