only occurs with sildurs. could not reproduce with no shaders or complementary.
Most recent release of bundled from modrinth, 1.17.1

sildurs high

sildurs extreme

no shaders

No, this would happen with Complementary as well if this was the case.

Sildur's Vibrant Shaders - High

Sildur's Vibrant Shaders - Medium

You are able to see the sky and celestial bodies behind chests.

with glass panes behind you can see straight through

does this happen with optifine?

try 1.17 optifine too

on 1.16.5 optifine (only one i have installed) it doesnt.
also it works without the glass, chests behind portal works just fine to reproduce

doesnt occur with 1.17.1 optifine

something must've broken since 1.17. can you restart your game and reproduce it (on 1.17.1 iris) with both sildur's high and extreme then send your latest.log?

https://paste.ee/p/8zcHw

wait my bad there was other stuff including some honey blocks in that world behind the portal

https://paste.ee/p/vK92H
heres one in just a superflat. First with extreme, then high.

Looks like it's CaffeineMC/sodium-fabric#38

No this seems like it might be something else actually, because it only occurs with sildurs and no other shaders