2 players. After ~10-15 hours ingame the game becomes literally unplayable due to glitched mass spawning of enemies and a "death zone" following players which causes random terrain to collapse. This happens both when hosting a server and renting a third party one. Having mods installed vs playing vanilla hasn't made a difference. The last 5 or so playthroughs we had all ground to a halt as soon as we encountered this. This has been happening since A17 at least, so it's not due to some recent update. The friend I've been playing with always reports that 7D2D continually eats up more and more RAM, eventually capping out at 16GB and requiring a restart, which sets the RAM usage back to ~5GB.
Building cut in half and slowly collapsing: