I'm still struggling with my dough being too soft to hold it's shape and little or no oven spring.
I really do think that I'm allowing too long for proof at each stage and indeed, my recent reading indicates that the time it takes for the double rise in the first sponge indicates how long the preparation should take up to baking the loaf. So, if my initial rise is 6 hours, then bulk proof, kneading, shaping. and all the mini rests in between should be about this time or even a little less.
I timed my sponge at about 5 hours to doubling. I let it continue for an extra hour and found that the sponge had collapsed at the 6 hour point. So, to my thinking, the much longer proof times that recipes have been telling me to use has done nothing except exhaust the dough. It becomes very wet and difficult to handle and there's no capacity for oven rise.