YourCoal

The following spawns on top of the bedrock roof in cave worlds:

fortress
igloo
jungle_pyramid
mansion
ocean_ruin
pillager_outpost
ruined_portal
shipwreck
swamp_hut
village

There are exceptions:

buried_treasure - chest will spawn just below the bedrock ceiling
stronghold - does not spawn at all

All of this applies to both when minecraft:caves and mincraft:nether is used for world generation.

The following spawns on top of the bedrock roof in cave worlds:

fortress
igloo
jungle_pyramid
mansion
ocean_ruin
pillager_outpost
ruined_portal
shipwreck
swamp_hut
village

There are exceptions:

buried_treasure - chest will spawn just below the bedrock ceiling
fortress - does not spawn at all

All of this applies to both when minecraft:caves and mincraft:nether is used for world generation.

I just recorded a little video demonstrating what happens.

https://www.youtube.com/watch?v=o-grR3yJcSo

I couldn't get it to replicate as perfect as I wanted, but basically it shows a freshly spawned entity (eventually) has the bug where opening its trading GUI will consume an item, such as food or equip armor. However, saving & exiting to the main menu and re-joining the world fixes it. This also happens on Multiplayer, however the difference is the server needs to be saved, stopped, and restarted and the same effect will occur.

While this video was recorded on 1.15.2, this problem still persists in 20w10a.

Still an issue in all 1.14 versions, 1.15 snapshots, and 1.15pre1.

I ran a test creating a new world with the seed "12345" and tested the FPS on it, once chunks loaded I averaged 480-550 FPS in 1.14.4 but only 220-250 FPS on 19w45b. (Core tested was an i7-8750H @ 2.20GHz)

Here is a quick summary of what I produced from this:
(link if photo does not show: https://prnt.sc/puc0mp )

If you have any questions feel free to ask, I want to make this is improved. 🙂

Can confirm this is an issue in 19w39a.

It was fixed to teleport you in front of the boat. By doing this, you will 1. not glitch within the boat anymore (hopfully), avoid the issue MC-153698, and 3. If you parked your boat correctly, should end up on land upon dismount now (which does work as intended now).

After some more testing, this appears to be all visible, not physical. As seen in the following screenshot, the mob appear to be clipping through the land: https://prnt.sc/p7xrak

However, You can place blocks on this "fake "entity, and it will not take damage at all, as seen here: https://prnt.sc/p7xrgg which I think proves that the entity is in fact where it should be, but visually is not updated correctly.

I have been unable to replicate on boats in old and new worlds, however horses in new words do this to me.

From what I can tell, if you begin riding the entity while the game lags, it will cause the entity to teleport back when dismounting. I simulated this by getting on a horse while new chunks were being generated, resulting in lag creation as I began to ride.

I went back and did "/playsound minecraft:event.raid.horn player YourCoal ~ ~ ~ 1" which I could not hear it at all, however after doing "/playsound minecraft:event.raid.horn player YourCoal ~ ~ ~ 100" (Setting volume to 100), the raid horn played as loudly as any other sound normally does when the volume is 1. 

I only figured out this after I cranked my Minecraft sounds AND laptop sounds to 100% when I used the command with a volume of 1.

Still an issue for 1.14, 1.14.1, and 1.14.2 versions.

Still happens with 1.9, 1.9.2

I can't get screenshots on here, it crashes my laptop.