Reproduce:

1. Enter a world with a PBR resource pack with deferred rendering technical preview enabled.
2. Spam the hot key to enable and disable PBR
3. Some chunks in the immediate vicinity will stop receiving visual updates.
(There is a blank PBR MCpack in attachments)

note: this also effects RTX packs. the only way to fix the broken chunks is to leave the area and reload them or rejoin the world (if you're unable to recreate the issue, try doing it in a superflat world with water everywhere it's easier to spot)

unlisted YouTube video (flashing visuals warning): Minecraft Preview 2024 10 09 20 55 20 (youtube.com)

(Adding a simple 0.25-0.5s cool-down to the toggle hotkey would fix this BTW)