The roller shutter box is not flush with the wall - possibly a planning error? Any ideas?

It depends: Generally on the coordination between trades, on relevant details, craftsmen are not informed about agreements and then they are away for weeks and the next trade is delayed......and thus unnecessarily much time passes.

So a general contractor who only does the shell construction themselves and does all the rest with subs (?) - who is responsible for the coordination there?

The cancellation of the exploratory trips would have hit us very hard as well. The general statement Corona/supply bottlenecks is annoying and for me comparable to a yellow sick note for lack of motivation at work – here just for service providers. As a client, you feel helpless – especially difficult when you yourself are a free decision-maker and creative personality.
Your house concept is so good and thoughtfully lived-through – once you are inside, it will work – a few details here and there. Then something that currently seems dull will shine again.

You really describe exactly the points that affect me.
Thanks – I also sign the last sentence and I know it... in my head... but it’s just like with a psychiatrist and his own problems or a teacher and his disciplinary problems with his own children etc. In theory you have the black belt...
As soon as the plaster is dry and a bathroom works halfway decently anyway, I’ll move in :D

So a general contractor who only does the shell construction himself and does the rest with subs (?) – who is responsible for the coordination here?

A small, regional general contractor who always works with the same local craftsmen. But our project is 50 km away, which apparently only now is noticed by some craftsmen. The general contractor is responsible... communication is however... o_O
A few trades are still missing, the rest will then be done by owner-allocated contracts anyway. We’ll manage that... the drywall installer is supposed to start on Thursday... supposed to.

A small, regional general contractor who always works with the same local craftsmen. However, our project is 50km away, which apparently only now occurs to some of the craftsmen.

At least probably with regard to the consequence that your construction site cannot be on the schedule with others on the same day. This is an important point @ all who are looking for a general contractor: that at the edge of their territory they sometimes have to work with other subs, or the usual ones are less flexible to reschedule.

Hello, with us the roller shutter box is flush with the inside and outside wall. On the inside there is a massive insulation block made of Styrofoam, integrated in the box. We have Beck+Heun boxes.
Best regards