Bubble wrap not sealed

This is just not finished, guys. Like a car with three wheels ...

shouldn't be a problem to fix that

is there something water-repellent on the gray base?

Exactly that is the right question and not whether the missing piece of the dimpled membrane is serious. A dimpled membrane is not meant to keep anything dry or protect against moisture.

I just have the picture right now.

I just see that it says you would have the possibility to buy the construction site.... Then the answer -> Take care of the important things first and get an expert, because you cannot distinguish what is important or unimportant.

That is something you can do yourself with [Bitumendickbeschichtung] up to [Perimeterdämmung] with 2 hours of work and a brush.