Minecraft v1.16.5
Forge v36.0.7
Framed Blocks v2.0

The Prism Corner is invisible when placed facing north or south.

Another couple of minor bugs is that grass blocks are not tinted when placed in a framed block, and the Framed Panel and Corner Pillar deletes the water source when first placed.

I cannot reproduce this on my end. Please provide a debug crash report (Hold F3+C for 10 seconds ingame) on gist.github.com, so I can take a look for possible mod conflicts.
Do you have Optifine installed?

Certain blocks deleting the water source is fixed in-dev, thanks for the info.
Grass blocks not tinting is a known issue, I have not found a satisfying solution yet.

Yes, Optifine is installed, although that's the only block doing that. I'll get the crash log

Please try without Optifine. I have no idea how their changes influence this mod and I have no way of fixing any problems caused by them.

Yep, It's caused by optifine. Strange how that is the only slope block affected.

Can you check if the Inner Prism Corner is also affected, please?

That one is working perfectly.

That's strange. I'll close this for now as wont-fix because I have no way of fixing stuff that breaks due to Optifine because they are closed source. Maybe I will look into this again in the future.

Alright, no problem.