The mod barely works in all 1.12 versions. When I make a new book, it only shows one character and whenever I get new books, they have that purple and black missing texture. Also, whenever I open the "Getting Started" book, it just shows a dot and nothing else. I just got a crash aswell:

fml-client-latest.log

O_o... Uh, I thought it was LiteLoader, but apparently now the game decided to fix itself as I put LiteLoader in and it all works now

This is properly because you are using Sponge. Try with just plain forge.

I'm not using Sponge, just normal Forge

Just saw that org.spongepowered was mentioned in the log.
It's clearly some other mods ASM that is causing this problem. Try without Optifine. If it doesn't work without Optifine then try without TTFR

I took out every mod except Guidebook, and it's still too small

There is something I noticed though, when I have the game not maximized (with both mods and no mods), it scales correctly

You never mentioned anything about anything being too small before now?
The scaling can be a bit wonky, that is a known issue, if that is all this is.

Oh shoot! This is the completely wrong issue! I accidentally posted my issue about the scaling on this issue instead of another one I was having before. Sorry for the confusion!

In that case I'm closing this.
It depends on your GUI scale and monitor size.

I thought this was the Guidebook issue I made moments earlier. I also just realized that I put the Guidebook mod to test that out instead of the Enchiridion mod. Sorry about that confusion

Huh, the mod seems to function as normal when I take out all of the various mods I have. I'm going to test and see if its the LiteLoader mod, which loads VoxelMap