Modpack version:
2.1.1

Describe the request:
In the overworld it is very noticeable that there are very few hostile mobs. If I compare the mob from DJ1 and DJ2 then in DJ2 there are almost no cave and surface mobs with no clear indication as to why.

Reasons why this should be changed:
There are certain quests that require hostile mobs (like King Crabs) that take a really long time to finish because the mobs just aren't spawning.

Describe alternatives you've considered:
For now we are still playing legitimately but might this issue persist we would have to cheat in the items or /summon the necessary mobs to be able to continue the pack at a relatively normal pace.

Additional context:
Server info: Multiplayer server, Hard difficulty, 32GB ram, Ubuntu server, High player cap.

I have the same problem :'(

Also according to someone on Discord, this issue might be caused by AbyssalCraft.

The more players there are on a multiplayer server, the more likely there's some random dark cave under someone's chunkloaded area that a bunch of mobs are refusing to despawn from and those mobs are eating up the mob limit. This is actually a common issue in other modded servers and even on Vanilla - one solution is to have a server plugin that kills all mobs counting towards the mob cap periodically.

There was only 1 player online during assesment

I can't increase all hostile mob spawns, just the ratio of certain hostile mobs vs others.

This is caused by the Minecraft mob cap, which (even on vanilla servers) causes very few mob spawns per player, if a lot of players are online.

Even with just 1 person on the server I am getting almost 0 spawns, even from day 1 of the server. In an irl week ive seen like 4 cave crawlers, an enthrawled dramcyx and a couple of spiders, I found skeletons and abyssal zombies but they were spawned from a spawner.

I've noticed a low amount of mobs spawning in our multiplayer server as well. We do have view range on 6 which could effect this. I know of some mods that could be used to adjust the mob spawns which might be useful? InControl! and IncreaseMobs

"IncreaseMobs" claims to work purely server-side as well, so you can simply include it on your server.

This is a known vanilla issue which affects all Minecraft versions that I know of, even up to 1.17.

You can try installing https://github.com/LXGaming/Sledgehammer (should only be needed server-side for this specific fix) and enabling the fix-impossible-mob-despawn-range and fix-mobs-not-despawning fixes in config/sledgehammer.conf. These are fixes I contributed back in the summer which attempt to patch the vanilla bug causing mobs to not despawn on lower render distances.

Note for Sponge users: you do not need this patch mod for this problem, as Sponge lets you reconfigure the despawn ranges for lower view distances.

We're having this issue - 2 players are on and we can literally AFK outside a night without fear of dying. We've very rarely encountered a hostile mob in a cave.

I came here because I've literally spent hours searching for king crabs. I've traveled 30k blocks looking at every beach I can find as well as going AFK for 90 minutes on a beach I know crabs spawn at. Nothing. I really do not want to spawn in items, but this isn't looking good.

Ok, I just went to an ocean monument and there were literally zero guardians. I wiped out the three elders and finished it. No chance any other player was there before me. Literally zero guardians are spawning. I can't even get 6 prismarine shards to finish the quest without doing another monument and killing 3 more elders, it's my only source.

P.S. This is even with "increase mobs" added to our server. I even bumped the default mob limits in their config. It made enough of a difference I could kill some crab kings but clearly it's a bigger issue than that mod can fix.

You might want to check the render distance your server has been set to.
If it is lower that 8chunks (8x16blocks = 128) then u might have an issue that mobs are unloaded before despawning properly, thus taking up the mobcap.

Also a nifty tool to check how many mobs are spawned is by typing in
/forge entities list

This will show you if any (and how many) mobs are spawned on it world

As said, try setting ur render distance to atleast 10 on the server so mobs can properly despawn and not hang around in limbo

Our view-distance was set to 6. I've bumped it to 10. We're a small community so that's probably fine but that's usually kept low for performance reasons. That, combined with the increase mobs mod, has made things feel a bit more normal. I'll try taking out the mob mod to see what the range increase alone does.