• MC Version: 1.16.5
• C&B Version: chiselsandbits-1.0.38-ALPHA
• Do You have Optifine: no

When I was trying to make custom windows using Managlass bits from Botania, it works perfectly fine but when I restart the game or just leave and rejoin the world, I can see the edges of the glass like this:

also works with alfglass:

Originally looked like this:

I have replicated this both in a modpack and with just C&B, Botania, and JEI. I have also replicated this bug with and without Optifine and Halogen. Is this a known issue? Is it an issue with Botania? There are no other blocks like managlass or alfglass I can try to replicate this with.

Any updates on a possible fix for this bug? Or is it an issue with another mod? Just to be clear, the border of the normal glass texture covers up the effect of this bug, so if the bug still happens, I can't see it.

I am not sure yet.
I was not able to look into this at the moment, since it requries a particular setup, and is a bit of lower on the priority chain for me.

My best guess this is related to the new off-thread model compiler and it being reloaded before those side blocks exist.
That said, can you load up the game, wait for the models to render and then press F3+T to check if a recompile of all caches works?

F3 + T did not appear to change anything.

This is not a problem with normal glass, because normal glass has a border around it while managlass does not. When I try using normal glass, the textures are not connected in the first place because bits don't seem to support connected textures. Managlass is essentially just a fully transparent blue tinted block.

Try it with normal glass?

There is sadly nothing I can do for you.
C&B Models support this up to a certain height, but there are some limits to how the system operates to not make it explode on the amount of resources it needs to consume sadly.