Mantaflow gas emitted on first frame of simulation only?

Not sure what’s going on here, I was playing around with timesteps, subframes to try to get smoke from moving objects to look smooth, now suddenly smoke is only emitting on the first frame of the simulation and that’s it.

I’ve pared my blendfile back, deleted the cache, but still getting the same behaviour. Here it is:
Smoke_Issue.blend (725.9 KB)
Have I done something silly or is my scene bugged?

Duh- set to geometry rather than inflow…