I've been making these loaves for years and never had this problem! For the last few weeks I haven't been able to get 1 single good loaf. They had lids on while proofing. They aren't sticky at all, although they look wet? I have never cut the tops cause the recipes have never called for it and it worked out fine before.
I have tried proofing less
I've tried babysitting my dough and using it as soon as its peaked
I've tried a different recipe
I've tried feeding my starter more
I've tried using my starter as soon as it peaks
I've tried proofing loaves overnight & during the day.
They proof with a lid on to avoid drying out
All the signs from the dough suggested this batch would be perfect until the loaf rise.
I think the first approach should be to lower the hydration. I say that because I had a sack of French T80 flour that behaved that way. I found that by lowering the hydration, the dough would act normally. There has a hydration level, around 60% for that particular flour, below which the dough acted fine and above which it became less and less able to hold up. Near that 60% level, the dough was very sensitive to even a few points variation in the hydration.
During discussions here on TFL, it was suggested that some aspect of the weather during one year's growing season might have made the difference. Although we can't know about your flour, it may be just as touchy about hydration. If you happen to be operating near such a critical value, a little change in the humidity, for example, might make a real difference.
Another possible source of unexpected variation could be the water itself. If its mineral content changes from day to day or week to week, that could make the difference, if you are unlucky to be operating right near a critical point.
TomP
At the first sight it looks like a dough tolerance issue, mainly a gluten network failure. A few more details could help to narrow down the details: amount of starter (in baker's percentage), liquid or stiff starter, flour type (only white flour or also something else), process details (mixing/kneading, temperature, bulk rise, etc).
Is breaking down. Might be the starter or over fermentation.