Nope. I triple checked and there's nothing (visibly) there. As I said, it seems to work if I move the staves to a different system, but they rebuild if I move them back.
THANK YOU MR. THOMSEN! The culprit seemed to be an issue with the grouping. At some point, I must have messed with the bracket hiding. Thanks!
Thanks, but I've reapplied "Hide Empty Staves" about a thousand time now.