Mine did this for a few weeks right after I got it, but turned out it was just a little off-track - the softer/rubbery stuff was smushed in the channel.
Once I realized what it was doing, I started pushing inward as I moved the switch (instead of flicking it with my nail, which I think lifted that end, making it not a level slide, and was what got it off track).
After about 10 slides that way, it slipped back into place, and has been smooth ever since.
