Comment by B1FIDO

They are not being marked as "Suspicious" but they are showing an infobox that explains they could not be scanned at all.

You could click "Seems Safe" on these messages, but they are not scanned by Google, and they are simply adding a disclaimer that they currently can't vouch for the safety of a message that they couldn't scan. It seems to me that this is a prudent and helpful course of action.