Flat sourdough bread

Hello all,

It's second time i'm baking bread from my rye sourdough starter. Im doing something like this:

day 1:

* take out sourdough starter from fridge

* feed it after about hour in warm place

* after about 8-10 hours when it's mature take 30 g of starter and prepare levain for next day (130g wheat bread flour, 10g whole rye flour, 90g water, 30g mature starter) and leave it in warm place for 12 hours (rest of sourdough starter back in the fridge)

day 2:

* 700g bread wheat flour, 70g whole rye flour, 510g water, mix and autolyse for about hour

* after an hour put 20g salt on autolysed dough, and distribute levain on top, mix together in bowl, then slap and fold for about 6-10 minutes

* 50 minutes proof, fold, 50 minutes proof, fold, 50 minutes proof and shaping

* about 2 hours final proof in basket

* bake for about 40 minutes in 240 C

Second time with almost the same recipe and my problem is that after I extract my dough from basket it starts flattening almost instantly, and it flattens for few minutes in oven, then it starts to rise and finally looks like on pictures.

Last week it had big whole through whole bread, but this week it have nice texture. but still too flat, not to mention no open crumb.

Also it raises like pita bread and final product looks a little bit like UFO (where it should look more like ball cut in half i believe). 

Additional problem is my round loaf cracked at the bottom and steam escaped through this crack.

Here is gallery with my today bakes:

https://imgur.com/a/76TsmXC

Also dough is very sticky, when i'm working with bread based on poolish or biga final product is really nice, but also while rising it doubles or more in size. With my starter I would say it rises about 1.5, 1.8. Is my gluten network too weak?

Do you have any suggestions?

Thank you !