I made a batch of stilton yesterday and have had the same problem with the curds not knitting together in the hoop.
I have made a couple of successful stiltons, but the previous effort I thought was a bit spongy. I wonder now if the problem was leaving the curds too long before milling and salting. The recipe calls for breaking the mass of curd up when the texture is crumbly, but this is a bit imprecise. Is it supposed to take ten minutes, an hour, three hours, overnight? I have read some stilton recipes which call for leaving the curd to drain overnight so I thought it wouldn't hurt to leave it longer than I had before.
But I think that was where I went wrong. I left it for around 2 hours, checking regularly and turning the cut blocks, which were still giving off whey. I think I should have milled much sooner, and not even bothered with the blocking stage.
I'll know for the next batch, but it's annoying as I had used double my usual quantity of milk for the first time. I have put the cheeses under pressure to see if it will help the knit, but somehow I think they will end up in the bin.