I think it's more than that, ymb. Short-term errors and unexpected events (ash clouds and so on) do happen. But this seems to be a longer-term problem: they're not paying enough (some even appear to be Uber pilots, self-employed) so off the pilots go and join Norwegian, who are also a low-cost airline but somehow manage to put them all under contract.
So Ryanair will have to raise pay - or find other ways of keeping staff from defecting - and raise fares to do so. And why not? Ummmm happily pays £9 to fly to Ireland. Why wouldn't she pay £10 or even £20? That's still dirt cheap, as long as nobody else is undercutting it (and I don't think anyone is).
Ryanair have just handled this unbelievably badly and infuriated staff, passengers and shareholders (shares dropped 3% this morning before climbing back a bit). It sounds as though they're still following the O'Leary mantra of attracting attention by making everyone hate them. But that's stopped working.