This has only happened a few times. I don't do the thumbnail test after I leave the 4k. And I generally don't do the thumb test once the blade starts getting close. And in my experience wire edges pop hairs incredibly well -- actually "popping" hairs is a red flag for me.

I generally strop the razor on a paper towel before I try any hair test to get rid of the water and swarf. I've always assumed that the leather stropping *really* got rid of any metal swarf that was stuck to the blade (martensite is magnetic).

Also, my hand american strop is getting darker on the side I'm using every day. *Something* is coming off the razors onto that strop.