I've been running this patch on my server for ~1 week+ (after making my own makeshift patch that did only the ItemFrame getItem() optimization, only to find out that someone else already had made the same optimization but better) and I couldn't find any issues, and it also improves performance a bit if the server has a lot of item frames (which is my case for a Survival server) by avoiding calling getItem(). Before the patch, all getItem()calls were using 0.25ms every tick. (not a lot but for big servers every optimization is a big W)

The only thing is that this patch needs to be rebased (again) for the latest version for it to compile, because MapDecoration's getType() is now type(): SparklyPower/SparklyPaper@27b4f21

Rebased for 1.20.6 https://github.com/SparklyPower/SparklyPaper/blob/ver/1.20.6/patches/server/0004-Rewrite-framed-map-tracker-ticking.patch

I was looking over this PR again and it seems like my approach here was a bit flawed, since it did not account for one framed map being viewed in multiple locations and being updated, only players viewing the item frame that's first in the entity iteration order would've seen the changes.

There are still some other gains that could be made, such as reducing the amount of map update packets being sent to players while no changes actually occurred, and the mess that is the tickCarriedBy (seriously, maps in item frames shouldn't have to check if the player is wearing a pumpkin).