Potatoes in pots completely failed

I have been growing Rocket potatoes in pots for a few years now and have had good results.  I always grow them from seed potatoes and put two in each pot.  I have 14 pots and have emptied 9 which have only produced two small servings in total. There seem to be some large earth worms in some pots and I did notice one wire worm in another pot.  Apart from some rotten looking spuds which I assumed were the seeds, there were also some containers with lots of small chunks of potato.  My questions are:  why did the crop fail this year and what is eating the spuds in the soil.  There is no evidence of anything burrowing in. The plants produced healthy green leaves but started dying back beginning of July which I assumed was normal.