The zombies often suddenly stop walking and the next second they appear some metres further. As if they're behaviour has loading problems.
But my server definitely has enough RAM.
Is this normal?
Is there a way to prevent this?
It gets annoying when they attack, the victim thinks he's safe 'cause the zombie stops moving but then all of a sudden appears very near again.
Sounds like regular lag.
Do you not see the same issue with regular players, or with npcs/htns spawned from outside BotSpawn?
No. Not that often.
Maybe too many zombies to load?
As I told, the RAM is enough for the server.
'Too many' depends on a lot of things but, if you're spawning a lot, limiting the numbers would be a good starting point.
See how it runs with only a few spawned.