My moss campions are also unco-operative little beasties. I have maybe a dozen plants and about 3/4s will produce flowers...some prolifically...others just a couple of buds. Right about now I give them a meal of diluted flower food...and keep them moderately moist. Definitely more moist than most alpines so I spot water them. The ones in full sun flower best.

Moss Campion seems to have the same sporadic flowering behavior in our nearby Rockies. There can be hundreds of plants in bloom among thousands for no reason that I can fuigure out.

Just a note: I don't like the plants that produce a zillion blooms but rather those that have no more than a dozen or so at a time. The fewer blooms show up nicely against the green cushion background. Also, they are a bit quirky 'when' they flower. Mine will start in about 2 weeks but there will be the odd bloom here and there throughout the summer.