1. What version of Minecraft, Forge and Mod are you running?
   1. Minecraft Version: v1.15.2
   2. Forge Version: v31.1.35
   3. Prefab Version: v1.5.0.3
   4. OptiFine: vHD U G1 Pre13
   5. OptiForge: v0.1.7
2. What type of issue is this? Choose one of the following:
   1. Bug
3. Prefab is not rendering the preview of the structure on my server.

• I suspect it's because OptiFine and OptiForge is installed. OptiForge is used so that OptiFine will work with Forge. It also requires MixinBootstrap.
• A similar issue was reported for Structurize at ldtteam/Structurize#112.

Optifine interferes with the shader processing at a fundamental level. Botania doesn't support Optifine with it's own preview features. Since the Structure Preview was based on Botania's preview function I cannot support it either.

Closing issue.

I don't have any shaders enabled, this happens with the default, I'm using Optifine for the performance improvements. And, from what I remember, it was compatible with Optifine in 1.12.
Does the no shaders make a difference?

I don't think so. I have never used Optifine since there have been tons of issues with it and Forge not being compatible with each other. I also honestly don't know too well how the preview works since I don't really do graphical engineering. I was able to tinker around a bunch with what Botania had to get it to work.

So basically unless Botania can get it to work; I simply won't be able too. Sorry.

Hmm, maybe the author of OptiForged can help?
He made a similar issue at ldtteam/Structurize#112.
But if not, I can do without.