Single Speed, chain jumps off rear gear, other than the obvious about chain being loose, any thoughts on adjusting? Its a 54 - 16 ratio. - Ta.

Is the chainline right?

This.

54X16 seems a bit of a jump ... may need more chain wrap on the rear cog. Have you considered perhaps dropping down up front a bit? Seems like a huge gear anyway. 1/8th or 3/32 DT?

I didn't read the ridiculously high ratio before, that could definitely be the problem.

my stab is 3/32"DT and flex in the front chainring is the culprit ...

Maybe poor chain line plus a stuck link somewhere?

Im using 52 x16 and with my chainline out it jumped. So it can be that factor.