Could be a bad batch from Chiner. Cheap pots are known for on/off and not true volume reduction
Sounds like either the resistance track is thin/missing carbon or the resistance track is warped? I use CTS, Bourns & Clarostat/Honeywell pots, those brands will give you at least 10-15yrs of hard usage, even more if you’re an occasional player? Have you tried cleaning them out with an aerosol cleaner, sometimes there’s a bunch of residue from the manufacturing process covering the resistance track?