Has to be catching/ rubbing on something. Could be a screw protruding in the threshold wear-bar. Any pics of the inside of your camper in that area could be helpful.
These newer style flimsy slide protectors I'm not a fan of.
Try prying back the wiper in that area. See if you can see anything.
What's on the floor inside in the area.
2014 LaCrosse 323RST-TE-C
2009 Chevy 2500HD Z71
R.I.P. Luke the campin dog