Is it a mod compatibility issue?

Yes

If it's a mod compatibility issue, please provide the link(s) to the incompatible mod(s)

Iris 1.6.17 https://modrinth.com/mod/iris/version/1.6.17+1.20.4

Minecraft version

1.20.4

Describe the issue

I've been using Iris 1.6.17 with the latest version of the mod and I'm getting this (what I think is a rendering error):

This issue is on Discord as well: https://discord.com/channels/662271867431682058/1208004064365912084

Which shader?

I cannot reproduce the issue with BSL shader. Does the issue occur with only iPortal, Fabric API, sodium and Iris in a freshly created new world? Which shader?

Which shader?

This is without shaders

Can you show a video of the issue? Does it render normally with BSL shader?