MinePro120

That still happens in 1.16.4, although more rarely, at least in the server version (Horse moved wrongly, that also results in a kick if allow-flight=false).

This should be marked as solved.

It could be a security issue if the hacker can change the book or something like this. Anyways, that's a whole other topic and I'm not sure how secure or not this is. Nevertheless, it is definitely inconsistent with what the signs do and I think they should all work the same way, whatever this way is.

Confirmed in 1.16.3

No, that's not a duplicate of those bugs. As a matter of fact,  I checked them before reporting and could not reproduce them in 1.16.3. Also, they use different JSON tags ("selector" and "score").

Version 1.16.3, I couldn't reproduce 😃. I noticed some weird behaviour though; when arrows hit the painting (or the half of the block the painting is on)  they just disappear, and (most of the times) the player takes damage as if they were hit by the arrow returning back to them (no matter the angle and only if the arrow was shot with the highest speed).

Setting level-type to default solved the issue. It wasn't an issue after all, just that in previous version of minecraft I didn't get any erros for my wrong generator-settings.

Good to know. This affects only items, not the respective blocks, right? I had some signs in my inventory that executed commands when right-clicked. It might have to do with that.

Just updated a server from 1.15.2 to 1.16.2 and I had :

Unable to resolve BlockEntity for ItemStack: minecraft:dark_oak_sign
Unable to resolve BlockEntity for ItemStack: minecraft:birch_sign
Unable to resolve BlockEntity for ItemStack: minecraft:acacia_sign

The warns appeared only once though. Is it something that could possibly cause world corruption?

Back when I created the server, I copied the world from singleplayer and set "leve-type" to "flat". I think, due to bug MC-134900, I wasn't given any error then (my "generator-settings" has always been blank) but now I am. Am I right? If that's the case, I should close this issue.

I found something! If the "level-type" is set to default (instead of "flat" that it was before) the message disappears. Is this expected behaviour though?

I have trouble recreating the issue on another world and thus it should probably be marked as resolved.

The issue persists on 1.16.2-pre1. Also, the paintings that become invisible, don't seem to have a hitbox.

Yep, I was working on a map too. Imagine dozens of painting becoming thin air by adding this tag...

Oh, because I saw many newer issues been given attention. Thanks.

What about my other issue? Will someone ever see it? I've seen many cases with issues remaining unanswered (by mods or official support).

I'm not a mod, but this (generally) is a performance or (according to the wiki) an upload speed issue. About the hardware part, test the amount of entities in your server. I once had a bug in my server (vanilla that is) that prevented falling blocks from despawning, so i had arround 65,000 falling blocks that caused massive lag (skipped ticks). I recommend using the arguments described here and Java Oracle (or OpenJDK) version 11. Reduce the render distance on the server side and check for other processes consuming system resources. But I really have no idea how the powerful systems mentoned above can be insufficient. Unfortunately, I can't test for myself on a powerful system. With a void world though, there seems to be no problem at all, even when having many cmd blocks running. Also, I've read that minecraft servers before 1.14 have no mutlithread support. And in the case of the guy with the Xeon, I've seen (cpubenchmark.net) that the cores aren't that powerful.

I can provide the world if the issue can't be recreated. I have to say, I couldn't recreate it by creating another server or in singleplayer.

Resolution : Turned out to be a performance issue. Resolved using optifine.

Here's the link.

Edit : I tried the same in the 1.14.4 version of the server (playing without optifine) and the results were the same. Seems like a performance issue. I'll be able to run the server on another machine in about a week or so, to verify if it's a performance issue.