PKHeX's frame detection isn't perfect yet, hence the flagging as fishy if it can't positively verify it.
haven't touched it for 10 months: https://github.com/kwsch/PKHeX/commit/3d7b2a2b29664428d53d8ef4e337f35e172a1eae#diff-0b0337837f9d5dc29e00fdcd5c73d009R50
probably not going to take another look at it for a while