Just changed from 1×9 to 1×10 and can’t get highest gear (smallest cog) to stay in gear.
Using an old Shimano XT triple on a Ragley Big Wig – checked end stop screws etc etc

Had no problems running 1×9 – is it possible the thinner chain and different cassette has revealed a chainline problem?
Can’t see with the naked eye anything obvious but interested to know if its a known problem and how to remedy.
cheers
Jim

Should be no reason why it shouldn’t work, running a 2×10 on a triple crankset without issue, and numerous ppl use triple with single ring. Tired mech (though I imagine you using a new one).. B screw or chain length issue maybe? You have used the std/normal spacer setup for the crankset, not tried to adjust the chainline by changing the BB spacers around?

Might take another look at chain length.
It is a new mech so don’t think that’s the issue.
Crankset is set up as standard, same as it was when running 1×9 – so other than changing the mech and cassette nothing else has changed…
cheers