I've been making sourdough successfully for many months now. But, my last few baking sessions have been a wreck! both times, when i make up the final dough (mixing in my mixer for about 7-10 minutes) it seems like nice dough, but, by the time it's gone through another rise or two it won't stretch at all. after it's been shaped and is in the loaf pan and rising, the top crust is tearing and getting crater like instead of puffing up nicely.
what's going on?