Moderator Note
If you are experiencing this issue, please provide a screenshot of this occurring while you have your F3 debug screen enabled.
The bug
Entity textures can break causing their textures to be missing several features or become swapped with another texture
Related issues
Attachments
Comments

We do not have enough information to find the cause of this issue.
Please force a crash by pressing F3 + C for 10 seconds while in-game and attach the crash report ([minecraft/crash-reports/crash-<DATE>-client.txt|https://minecrafthopper.net/help/guides/finding-minecraft-data-folder/]
) here.
This issue has been temporarily closed as Awaiting Response. Once the requested information has been delivered, the report will be reopened automatically.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – ✍️ Feedback and Suggestions – 📖 Game Wiki

Have crashed world where this bug happened and attached the crash report,
can however not recreate this bug after restarting the game & launcher. It had worked 2x without restarting the game

We're unable to reproduce. Please try deleting your assets folder and try again.
If you're unable to locate your assets folder, please check out this link.

If you are experiencing this issue, please provide a screenshot of this occurring while you have your F3 debug screen enabled.
@Adrian: For most users, this is a temporary issue, and a restart fixes it, based on the reports I just linked to this.

It might be useful so I'll put it here. I made a crash report after I saw that the world icon had a minecart texture. I don't know if it's the same problem but I'll rather put here the crash report that I made by pressing F3+C. (It's the report from June 30th.)
Removed a modded screenshot.
I can confirm that this issue is present in 1.16.4. This may be hard to reproduce as there is no "set in stone" reproduction steps as this seems to happen randomly.
Can confirm that this issue is present in 1.16.5.

Requesting ownership as the current reporter has been inactive
Can confirm that this is still an issue in 21w07a. I've attached a screenshot.
I've attached an additional screenshot of this being seen with a creeper along with a creeper head.

This is caused by model corruption, if you encounter this bug, the model is broken

Can affect GUIs as well.
I also found steps to reproduce. We have to reload the assets a lot. Have done this with datapack selection menu, but we can assume it may also occur after a lot of resource pack reloads, however this needs to be confirmed.
Notice these steps almost definitely are not the only way to reproduce this issue.

My rain has become the black cat texture. This is vanilla with default resource packs. This rain was summoned in though with '/weather". I don't have one with the F3 screen open as I stopped the rain with commands. I did open it and there was nothing special about it, just rain. This happened to again though (on 1.16.5 this time) though it stopped happening after that.
This is similar to MCL-15593, MC-198710 and since there were said to be duplicates of this I didn't create a new ticket
@unknown, the UIs being affected by a similar issue is in fact MC-181280.
@unknown, the issue with rain is MC-189979, I've removed your attachments from this ticket to reduce confusion
Can confirm in 21w08b.
Can confirm in 21w11a.

I have had this same problem for a while now. I have attached screenshots and a crash report. The first image is guardians, while the second is a cat. Do note that sonly some of the cat textures were messed up, while others were normal. also, When I create and join different worlds in the same session, some mobs are affected in one world but not others. Some mobs I have noticed, particularly horses, will have completely different texture errors every time I see them. Also, after restarting the game, the guardians returned to their normal texture, at least for the time being. If there is anything in particular I should check, please let me know.

I should note, I have completely reinstalled Minecraft and the issue persists.

Can confirm in 1.17-pre1.

This possibly happens because if 2 or more entities spawned on the exact same frame, Minecraft fails to specify the second RAM pointer which makes RAM pointers to add them in the exact same place where the entity graphics pointers are located. If you encounter this in vanilla Minecraft, then you know this was the cause.

not sure if that's related, but I get output log flooded with this message when this issue occurs, what causes massive performance decrease
OpenGL debug message: id=1282, source=API, type=ERROR, severity=HIGH, message='GL_INVALID_OPERATION error generated. Texture name does not refer to a texture object generated by OpenGL.'

I also have this problem

I have the same issues. These are all different save files. No mods/texture packs installed.
[media]
I have also done a full uninstall/reinstall and nothing changes. I didn't have this issue before 1.17.1

Dupe of MC-181280