I thought I noticed a fix for this, but maybe it was reverted. So I tried it on a different Character Creator character. So I tried it on an edit I made of Steve.
As you can see, it works just fine. And I changed some of the clothes to match the one on the character on the top image to see if that was the cause of it. I think I was wrong.
Duplicating the world I observed the issue on and getting rid of all behavior packs on that world but leaving “Minecraft Classic Texture Pack”, the only resource pack enabled that wasn’t tied to an add-on, it may just be an issue with that resource pack. They still disappeared when I got too close with that resource pack still enabled, but they stopped doing so when I disabled it too. Is it still a bug that warrants being fixed?
Here is the Superman shirt with no visible sleeves. I also made sure to capture the icon of the shirt that depicts it with sleeves.
I have yet to figure out which items make the sleeves not render. I was wondering if it could be tied to that character of mine rather than items, but I don’t exactly want to delete and remake that character to brute force it until I find out. I know that’s not what you’re supposed to do when debugging.