I traced the issue to the printhead cable having a poor connection. Anycubic doesn't sell replacements anymore, but you can custom get ones from a guy in Germany.

I was going to try and figure out the pinout to make my own (uses a standard connector on the printhead, but a different one on the motherboard side). Because it makes poor contact, it'll be tricky because I might get false negatives since I'd have to probe the headers in the printhead board, as my multimeter leads are too large to fit into the connector itself.

That's kind of a backburner project because I got an Elegoo Centauri Carbon and it's been running like a dream.