Without images showing your problem or a way to reproduce your issue step by step, it won't be possible to help you fear further.

Ok, I made a short video to show how grouping works on my system and you can have the model if you want to reproduce this on your system.

https://1drv.ms/v/s ...

The primary criterion for drawing order in the plan is the elevation of an object or a group of objects (the elevation of a group being the smallest elevation of the objects it contains), then the second criterion is the order in which they appear in the furniture list when the list is not ordered ...

Maybe yes, but I do not add items one by one. I mark a bunch in the plan and create a group for it.

Normally I see in the planning view the topmost parts on top (visibility is top down), but as soon I put them in a group i see the bottom parts on top (visibility is bottom up).

Is this intended or a bug and how can I avoid this behaviour ?

As you noticed, groups are exported, expanded or not, as they look in the furniture list.
It's probably something which should be improved, moreover since there's no way to distinguish a group from other items in the CSV file.
As I don't know that much how people use CSV exports, it could be also ...

How can I export all entries to a csv without expanding each group manually ? Sadly there is also no "expand all" and I have to step through all groupings to expand them all for an export.

Thanks for an answer that works.

But why is it then described and possible that there are levels beneath the surface that are not visible ? That doesn't make sense to me.

I am designing a motorhome and added recently the chassis to the design because I have to place some components into the chassis. I think this is similar to a cellar. I added a new level with negative rising as described in the manual. That works so far, the level is on the first place, I can place ...

I am new with SweetHome3D and I found two situations that I don't know how to solve it. Both have the same problem: When defining a wall, i can set the hight at the startpoint and at the endpoint. This will result in a wall that elevates from the ground to top like a ramp. But in my case, the top is ...