Template Style - Modules can't be customized

Hi all,
I just installed 1stclass template in my present installation.
When I want to modify modules in template style I only see an empty list.


Later I installed the template demo from quickstart package.
The I can see the module list appearing.


Both installations are Joomla! 3.8.1.

What could cause the different behaviour?

Thanks in advance!

You can only modify the modules if they are available.
If you have no modules in your clean Joomla installation, there cant be any module to customize!!

This is no clean installation.
It's an existing website with over 40 public modules.

Not all modules are linked to 1stclass modules positions. But about ten are - that's why I'm wondering why these don't appear in template style.

Yes youre right.
But maybe your modules are not published on "our" module positions like:
- top-a
- top-b
and so on....