The end portal and end gateway shader effect seems to break after exceeding a certain height. I can not really determine the pattern but it seems to unload partly without a reason to unload.

This issue only exists when optifine is loaded via optifabric. Optifine alone does not has this issues

https://cdn.discordapp.com/attachments/896862947480068137/1152330289247436890/2023-09-15_21-43-34.mp4
(video too big for previewing)