When running my fully modded install, chains connected on fences seem to only render from one side.

MC 1.16.4/5 (both versions)
Forge 35.0.37/36.0.1 (both versions)
connectiblechains 1.0

https://imgur.com/a/96cJYce

This may only be marginally helpful, since this doesn't happen with just connectiblechains by itself, and I can't seem to pinpoint the mod combination that actually causes it. I'm taking a wild guess it has something to do with optifine, but it doesn't happen with just optifine+connectible chains. I also went through and put 30 mods in at a time in chunks, alongside connectible chains, and I couldn't reproduce the issue.

This is the list of 152 118 60 34 mods I've trimmed it down to so far from 210 where it still happens: https://gist.githubusercontent.com/phyne/8b9c6ecf1000de2bbb2637d6f74bae5e/raw/a67abb0903f4b2775d51dad78b0c9c561a469ba3/mods.txt

?!?!?!?!

Idk man... hoping there's something relatively trivial on your end that'll fix it. If not, I'll keep going one by one to pin it down.

Ooooweee, Ok. Looks like it's a combo of immersive portals, and optifine, should have known...