It is a WARNING,
not an error,
just a heads up. I trained my eyes to ignore the ones I know about as being harmless.
HIDING these is a
terrible idea. We forget that we made settings
to Calibre almost a decade ago . Suppose you change devices (or reading apps), and all of a sudden the books that have "PASSED" with a clean report, start failing.
What!
OMG, I hid that warning a long time ago.