module M = struct exception E end
let _ =
  match () with
  | () -> ()
  | M.(exception (E | Exit)) -> ()

generates instrumentation that includes the case | M.(Exit), which then triggers

File "test.ml", line 5, characters 2-26:
5 | | M.(exception (E | Exit)) -> (
      ^^^^^^^^^^^^^^^^^^^^^^^^
Error (warning 33): unused open M.

The solution is probably to suppress warning 33 in the suppression list here: