I think I may have stumbled upon the same or a similar bug.
I have a 8x8 wall of (glowing) signs that display stats for my horses. I use culling mods and my FPS drops from 300 to 20 whenever its in my FOV.
I first thaught it was the horses but after testing i am fairly certain its the signs.
This issue was introduced 2 days ago for me, after we updated our server to 1.21.11. We where on 1.21.4 before this, and i had no performance loss with the older version.
Just want to show how small it is on screen in a world on mobile you can see just how much smaller they are. You practically having to use you’re pinky to press every item and how small your item bar is even the games sitting buttons on the top of the screen. You can see the big space you have around the actual block menu.
Agreed even in game your storage and bar are to small and even in the first time playing the update it was already frustrating pressing for a item, in extremely annoying and frustrating and unplayable not even enjoyable for mobile players. I hope this is five and get our old game screen back where the buttons are noticeable and playable.
For me this crashes the game, with error code 11