Tstu0001

The issue appears to have been fixed after 1.16 was released.

There seems to be some positive changes to performance 20w10a, but this issue is still noticeable.
I would honestly love Minecraft to use more of my GPU than a meager 32%

Edit:
In all snapshots, I found that pausing the game instantly stops the lag issues I have in game. In some instances it may lag immensely in the menu. Changing the render distance to any value stops the lag from there, but that is a temporary fix. The game will occasionally drop to an unplayable framerate regardless of what settings I change seconds to minutes after doing this. A small render distance and minimal settings does little to solve it.

In 20w09a, the performance drops are identical to 20w07a and lower for me

This is happening to me too. I normally get 237 FPS when playing the snapshot, when loading chunks, the game slows to a crushing 12 FPS to 3 FPS. Much more than noticeable. It's practically unplayable when it happens, which lasts for about 8 seconds then returns to a playable framerate.

I've noticed this occurs when large groups of mobs in the Nether appear with the new spawn mechanics and reducing the render distance to less than 5 reduces the impact of these framerate drops.

I uploaded it now. To demonstrate with the addon, you will hear a pigman sound when you spawn either a horse or a skeleton horse. With the zombie horse, it simply spawns a zombie riding it.

Hopefully this helps

There is also the issue of lack of documentation giving not enough information. I'm struggling to understand why the devs set up mobs to use strange names instead of what they should be indicated as.

There should have been more clarification on "entity_type" and the values that are acceptable.

Addons are getting more frustrating than fun to make now.

I've tested this in multiplayer. The tick speed reduces to an unbearable crawl with the only way to recover is through killing all mobs with this behavior. The tick speed reaches to a minimum of 1 tick per second. Completely unplayable in a large server, but does not immediately crash fortunately.

Holy crap this bug is incredibly old. Since Nov 2019 and still present to today

It almost looks like it, but this is an entirely different issue. This is more of a conflict between functions and chunks not working well with each other than more of that bug.

I can confirm it breaks /setblock and /fill

Sometimes half or small sections of a structure will generate and other times it works correctly. What happens seems to be dependent on how fast chunks load and the complexity/size of the function file being used. This is not good at all for anything server related 

Summoned entities also might be affected by this. I have not confirmed that yet.
Confirmed! Entities are also affected by this!

I know that blocks set and filled outside of render distance's generated chunks are set to not work when "outside of the world", but there is no check in place to determine if the player is nearby where the blocks are supposed to be created.

I see. That's some extreme inconsistency I see. I never noticed that has ever changed. I always assumed "minecraft:" would have been the standard even if its functionally makes no sense just like with entities. ([*cough]* bees don't do it though)

The identifiers for adding blocks in addons implies the same thing

Does this mean entities will eventually be disallowed that "minecraft" part too?
(It does make sense to have it available if addons have a chance to use it, but I'm seeing fractures like this and it makes documentation and possibly distinguishing between addons and minecraft much more confusing.)

Forcibly disabling Web Account Manager service solved the problem! I'll be reporting this to make sure nobody else has to encounter this in the future.

This problem of too many particles being rendered is also the cause of multiple large nether portals causing the same framerate problems.
If the stars created by the end portal are considered particles, that might also explain the lag when you look towards the horizon of an end gateway portal.

The amount of particles were supposed to be regulated by the particle render distance, but it seems to only limit particles far away, which is not helpful.

I just tested it on all devices including a gaming computer. Same outcome. Intense lag. Too many particles. At least have the particle render distance work to prevent a threshold of particles from appearing instead of having everything render within a certain radius. 😞

This has caused many problems which make multiplayer more difficult to work with.

Yes, both use the same version of Minecraft Bedrock Edition.
The chromebook uses Minecraft as if is an android phone with laptop features. It definitely looks like a compatibility issue is going on somewhere.

Me and my brother could not play multiplayer, because of this issue. OS updates did not fix the problem.

Seriously, nobody is doing anything about this?
Welp, that is majong's bug tracker in a nutshell.

Nobody wants to address this issue?
This bug does not happen in Minecraft Java Edition.

Build: 396272
Build Date: 2017-06-27

This issue is easily reproduced when using the old setting for a world. It is rare to have this issue in infinite worlds for some unknown reason. This could be an undeleted feature from an older version of Minecraft.