Found this site searching for "loose arbor nut." A couple of years ago several subscribers mentioned that the arbor nut on their DeWalt jobsite saw (DWE7491) repeatedly came loose.
Unaware of this, I just bought a used one and discovered that my saw has the same problem. As a second owner there is no warranty coverage, although I was sent a replacement arbor nut. Didn't help.
So I replaced the arbor nut and also cleaned the shaft, washer, nut, and blade (blade had a little residue from resin removal), but none seemed to have oil/grease on them. Checked threads on the arbor and they looked fine (not a machinist, though, so check was just visual). Started saw a couple of times following that and nut remained tight, but didn't try to cut anything.
Did anyone find out, definitively, what causes that problem and what it takes to fix it?
Is there a response/acknowledgment from DeWalt about this problem? Dewalt rep I talked to suggested taking the saw to a service center.