The main cause is usually a bad design of the map, with too many independent entities, usually unnecessary, such as excessive light sources in The Hive, many of them on a tunnel where we go inside a vehicle from which in theory you cannot see the lights. However, these plugins add entities and can be the straw that broke the camel's back, and ends up filling the limit of 2048 entities that Left 4 Dead 2 supports.

- Thirdperson RE6 mod or similar
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2780173405

- Luminous checkpoint arrows mod and any other mod that adds props with animations or lights:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=934602353

- Dynamic light and other mods that adds lights sources:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2261165699

- Active talkers via scripts:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2696358865

- High commons limits, as z_background_limit or z_common_limit above 40-50. Restore cvars to original values to solve.



With metamod-sourcemod, this plugins can help, but It's not perfect, it just reduce the chance, but it can still happen. You need to know how edit and recompile by yourself. Erase this line of the source code.

HookEvent("teamplay_round_start", Event_RoundStart, EventHookMode_Post);

And recompile. Now works for Left 4 Dead 2.

https://forums.alliedmods.net/showthread.php?t=265902