Never seen this happen - I can't offer any explanation - just replying to send my sympathy. Primroses here have been better than ever. If you need any replacement plants send me a PM.

Maybe something's nesting in there - voles? ground bees? rats? Depends on the size of the holes. Though quite why all the primroses wouldn't grow is not really explained by that, you'd expect some to still grow. Are the holes where someone's come along and dug them all out?

I agree with Bamboo it sounds more like the human type of predator than the animal sort. We have various birds and animals that create holes in the ground and rabbits will eat off some plants but they leave a scrape rather than a hole and you would assume that they wouldn't be that meticulous and eat all the roots of the primroses! Deer of course eat lots of things, but again I think you would notice other signs of them. Mice and voles burrow under our grass but leave neat little holes so you know what they are. Can you inspect the holes and see whether they are scrapes, neat round holes or the type with trowel type sides where the plants have been removed? Are they in a position where someone could get to them?

If the bank isn't open to the public, the only explanation I can see is, although most unlikely in open ground, then a vine weevil attack. This would be a result of their actions in late summer. I would wait to see if the dormant seeds from last year's flowers have begun to germinate as they usually come up like weeds.