From proof to oven, rise lost

I posted on this thread; but I suspect it's too old :-)

I've been using Ken Forkish' Flour Water Salt Yeast - working my way through to biga using mostly KAFs and Bob's Red Mills.

The only thing I have not done is preheated my Dutch Oven - so far!

Although I now get a great rise, my proofed dough tends to collapse when I invert the banneton and place the dough - very carefully - into my Dutch Oven.

Is it that:

I need to be more dextrous/careful; or
the structural strength still is innately poor - I'm still experimenting with the length and frequency of folding?

Thanks for any advice!

You might be letting the loaves rise too long as well.

Thanks, Placebo. I'm actually following almost to the minute what Ken Forkish suggests…

seem to spread before they puff themselves up. I'm always saying to Lucy after I slash one and it deflates 'here's a Frisbee for playing with later'. Sometimes, when they are really over proofed a lot they are bricks too. Best to keep a close eye on the proof and don't let it get past 90%,

Happy Baking

Wholemeal.

I guess I should try under proofing a little next time - just to see.

Thanks!