After some more testing turned out: The reported bug is present under the following condition:
- The neo2 keyboard layout is set as 2nd or above keyboard layout, with main system keyboard layout set to something different. - When neo2 keyboard layout is set as first and main keyboard layout, and only then, the levels 4 and 6 are accessible as expected. Erratum: the modifier combination for level 6 is apart from what I had written in my original report not shift+modifier4 but modifier3+modifier4. This doesn't change things, the levels 4 and 6 are merely accessible this way when neo2 is set as FIRST keyboard in system. Additionally it turned out, if the numlock key happens to be active when switching to neo2 layout, the keyboard is locked to layer 4, no way to escape to other layers, besides switching to another layout, deactivating numlock, and switching back to neo2
