Symptom Identification (Help needed)

Hi! We are having some trouble identifying what is going on here and would appreciate some help!

To be brief but put things in context:
We are growing autoflower strains
Outdoors at a mediterranean climate, although we are hitting pretty high temps (over 30 degree Celsius)

We are making sure not to overwater nor underwater because we've had that before, so we dont think it is that but could be.

Here are some photos,
We have more than 10 plants and this morning, almost sudenly 4 of them had diverse symptoms
The most common being:
- Leafs heavily drooping
- Weak and feble main stems, on of them was actually "broken" in half like from weight
- One of them has all of a sudden brown stains from the inside out and is definetly dieing fast

Here some photos:

We are not using extra nutrients since autos are not so hungry, we are using top crop (the least charged one) substrate and some worm hummus. (Not much)

They are 3/4 weeks old, we planted them at different times.

 

More photos.

Anything i might have forgotten and could help just ask me

Also english isnt my main language so there might be some mispellings etc