In my logs, I noticed a block of text stating the it should be reported to Quark. I'm using Quark-r1.6-177 on Minecraft 1.12.2. In the output, I see LibrarianLib mentioned among other mods (OptiFine, HammerCore). I'm assuming it's an issue between Quark's rune enchantment effects and LibrarianLib's enchantment glow handler though?

https://pastebin.com/VrE54EX6

To be honest, I don't think I'd have ever noticed something failed if I hadn't been snooping around in my logs for another issue so I'm not entirely sure what is broken.

Nope, this is HammerCore, not LibrarianLib. I wrote both ASM targets, it's not likely that they'll conflict with each other.