Shimano 1×11 XT upgraders have been suffering this 1x backpedal issue for ages. Also on Next SL cranks but it happens on an SLX triple (1x in middle position) too. It annoyed me enough to go back to 10s but retain the 11s shifter and mech. I was considering a costly switch to an xD driver and SRAM GX cassette on my wheel but I think I’ll leave it since I’ve more or less sorted it and not lost any range. I’d not heard it being a common issue with the 1×11 SRAM setups but enough of you have it as well.
10s XT cassette + 40T expander on one bike.
11s XT cassette, remove one cog + one up spacer behind 1st + 18T cog kit.
I was in a bike shop recently there was a nice shiny new free standing Shimano 1×11 setup bike, it had a RaceFace crank and SLX cassette… that also dropped on back-pedal in 1st. 🙁