I just went back to the original database, with the errors. I performed the search, altering the column name, cycling through each of my real custom column's names. I got back 26 responses for one custom column (#universe), but none of the books shown were the titles that caused the error.
I also tried to edit the metadata on the 26 books. The Edit Metadata screen appeared without throwing an error at all. Perhaps, since I'm now using 9.14 and that should include the fix you mentioned, maybe calibre is handling things internally properly? So these "new" errors are not occuring, but the old ones exist in the database already, thus the continuing complaints?
Would your fix require previously "damaged" entries to be corrected manually, or would the correction be done in some automated fashion?
BTW, I think I found another error with composite columns and series/series_index. But one error at a time.
