Having played and beaten all the base game Elder Gods I recently bought the Cthulhu expansion and am currently in the second part, having acquired enough investigation to reveal Rlyeh. I currently have red and yellow glyphs locked for ALL adventures, not just Rlyeh, but no monsters or locations seem to be causing this - no colored circles, and I have double checked all adventures and monsters. I also have glyphs for the amulet which should allow red glyphs and spells to be available. Is there anything else which could lock glyphs like this or is this a bug?

Well, after I quit and reloaded the glyphs had unlocked themselves somehow! Shame I'd already thrown my best characters away by then. This is definitely a bug, perhaps related to the appearance of Rlyeh, since this happened after that. Hope the Devs can look into this for the next patch.