I recently converted my '09 Stumpjumper fsr from 3x9 to 1x10.
I went with a 32t RaceFace NW ring, everything else XT including a 11/36t cassette. I just converted that also with a 42t Wolftooth GC, OneUp 16t (removed the XT 15t and 17t) and their Radr cage for the XT Shadow+ derailleur.
While running the 11/36t cassette (about 500k's total), I dropped the chain once. It wasn't particularly rough terrain at the time, so I was a little confused. Where I live it's pretty steep (Canadian Rockies), and I found the 36t tough sometimes so I did the 42t swap. This meant adding a couple links to the chain, which may have contributed to dropping the chain 4 times on it's maiden ride... The chain is as short as possibly safe with the rear suspension completely bottomed (chainstay length grows 15mm).
Each time it dropped, the terrain was fast and rough, so the chain was down on the smaller gear end of the cassette. It really pissed me off, like when I used to run tubes and I'd flat part way down something fun. I checked the clutch in the derailleur and it's fine. Maybe the chain gets a whip in it as the rear end extends (chainstays shorten) and I slightly backpedal to set up for a corner, dunno :noidea:
I just ordered a Moove top chain guide (BB mount), so we'll see how things go once that's fitted. Fairly disappointed, as I'm apparently the only guy around town that's having this happen.