Version-1.16.5
Mod Version-0.3.4
Optifine-Yes
Reopening a world save or restarting a server makes some chiseled objects change their block type and texture. For example on my single-player world, I had a railing made of dark oak wood and black concrete (both vanilla) but when I opened it later the concrete changed to light blue glazed terracotta (also a vanilla block) but the dark oak wood didn't change. Just now I restarted my server and a statue that is made of multiple blocks had one type of block change to the bricks used in the floor. This does not just affect the singular block but all the blocks like it. Just to reiterate, it's not a visual glitch with the textures, it changed to a different block type completely, as if you break off a bit it will be light blue glazed terracotta not just black concreate with a different texture.

Fixed after updating to the latest beta. Can still occur once during the update process.

Same problem! friend updated our server and its modpack, and now my glowstone tiles became dark oak half drawers?

I see that this is tagged as "On Hold: Rebuild". Is there a Discord server or someplace where we can go for updates on the rewrite?

https://discord.gg/G4rcMbxQ

Yes
The discord already contains a test build, which is incomplete.

Can confirm, had this issue as well on a server I play on.

modpack Valhelsia 3 (version 3.3.0)
minecraft (version 1.16.5)

I have the same issue. The block type and color of chiseled blocks changed after I updated Valhelsia from version 3.2.0b to 3.3.0.

This happened to me too! and then everything that changed, is now gone

This also happened in Enigmatica 6 between update 0.4.8 and 0.4.9, C&B version 0.3.4 in both modpack versions. We added several mods in 0.4.9, I'm guessing that's the cause.