Strawberry plants- what is the problem with them, can anyone advise, please?

I have two pots with strawberry plants (different varieties), in different parts of my garden, both in full sun all day, I've had them for a couple of years and they've been fine. But although they were doing really well this year, they then went downhill, and the leaves got more and more like lace until the whole plant was like it and the strawberries didn't survive. I bought another very healthy looking plant and put it in another part of the garden, more in the shade, and in the border, not in a pot. Since then, the leaves have got more and more lacey and now that too looks dead and the strawberries have perished. Does anyone know what is causing it, and can advise me on what I should do, please?