Similar to https://git.cacklingfiend.info/cacklingfiend/lignumis/commit/d508b90ad745e452026b9fb851444f12d52487a3 and https://mods.factorio.com/mod/lignumis/discussion/67a7c569339eb9750bca33a0, I think epic-quality needs to be handled here to support the Quality Assurance mod.

Why is that? If legendary quality does not exist as a technology, it will be removed and Quantum processor technology remains as prerequisite. Isn't that still suitable when epic isn't available as well?

Not a modder, so not totally sure how everything works when modifying techs. Here is the error when trying to load both mods: https://i.imgur.com/P23S6Kt.png

Quality assurance gives both epic and legendary quality research when another technology (configured by the mod settings) is researched (i.e. Automation, Automation 2, Quality Module, etc.). Maybe the way that Quality Assurance modifies both epic and legendary research is causing the issue?

Currently I don't see it. Everything seems to work. Lignumis does not interfere with epic quality.