Before reporting, make sure your problem isn't caused by the game running out of RAM and you have read the installation guide carefully.

• Yes, I'm sure this problem isn't because my game ran out of RAM.

Describe the bug
Going into the Tofu dimension and teleporting back with the mirror makes entities disappear, both in the Tofu dimension itself and in my base too.

Details:

1. I went into the Tofu dimension through the portal and down a cave. I activated a monster box which spawned spiders that webbed and killed me. When I went back down there the mobs had disappeared but I was still getting webbed and damaged, I died again.
2. Now back in my base I noticed how all my animals had disappeared as well. Disappeared as in invisible both in the game and on the entity radar, but their sounds could still be heard. I did however not "feel" them either when going into the enclosure.
3. After restarting the game the animals were back as if nothing had happened. However in the Tofu dimension when I got near that area where the spiders had spawned I was still getting webbed and damaged without anything ever showing up or being there.
4. So back again in the Tofu dimension I used the emergency item to kill all hostile mobs. It did not work, I was still getting webbed and damaged. Swinging my sword around me did not hit anything.
5. I teleported back to my base, my animals had disappeared again. However their sounds had disappeared too and they didn't come back when I restarted the game. I presume this is because between the first and second incident I set my base to be always chunkloaded. However I only killed hostile mobs, not all mobs with the emergency item. Anyway, the problem is still there and now I have lost all my animals to it.

To Reproduce
Steps to reproduce the behavior:

1. Go into the Tofu dimension.
2. Break a monster box.
3. Die or teleport back with the mirror.
4. Go back to where the monster box was and/or check on your animals.

Not sure if this reproduces it for anyone else, please see my detailed description further up for more details.

Expected behavior
Enemies should either completely despawn or be actually there, visible (unless with status effect invisible) and damageable.
Persistent creatures like animals should never despawn or become invisible/untraceable.

Details
Please fill out the blanks below:
Modpack Version: (1.35.2.118.1)
Did you add or remove mods? (no)
Did you edit any config or script? (no)
Using shaders? [Write 'Default' if you are using default shader, if you are not using the default shader please write the name of the shader you are using.] (Default)
Singleplayer, LAN game or server pack? (Singleplayer)

Additional Info
I have experienced occasional crashes from Xaero's Minimap (and Dynamic Surroundings?) as referenced in this bug: #123
I don't exactly remember if one of those crashes and my issues coincided at some point as the first parts happend several days earlier to the last part which happend today.

This is a Common Issue in Modded MC, its just a loading error
for some reason these Entities are not rendered for the Player, they are not invisible
Re-Loading the Chunk fixes it usually

Here's some more information.

After some issues I reinstalled the pack and copied all files over.

Today I went back into the Tofu Dimension again, and encountered a few invisible entities, however I could all kill them. They happened to be big Tofu slimes which became visible once they broke apart the first time. Maybe a texture is missing here? I found no spiders and no other invisible enemies.

Animals in my base still turned invisible, but I was able to identify the conditions for when it happens now:

• The chunk in which the animals are must be chunk-loaded (set with the FTB tool) when going into the other dimension.
• It happens with the Tofu Dimension and the Abyssal Wastelands, but not with the Nether, Aether, or Twilight Forest.
• When they have turned invisible using a waystone to teleport somewhere else in the Overworld and back turns them visible again.

So the workaround for now is to not have the chunk with the animals loaded when going into one of those dimension, or to not have it set to chunk-loaded at all.

I see. I haven't encountered this before in any modpack so I wasn't aware that happens more frequently.