I think I was able to somewhat fix it by this point.
In the Expression Maps setup, in the right bottom corner, you have the Articulations list. And there are many articulations, however, only a few of them have "Type" = "Attribute". Only those are displayed in the Articulations dropdown menu in the upper part of the Key editor. Others have "Type" = "Direction" and they are not displayed in the Articulations dropdown menu. I changed all types of "Direction" to "Attribute" and they are displayed in the dropdown menu now. And they work.
The difference between them is:
If you select Attribute, only single notes are influenced by the articulation symbol. If you select Direction, the articulation symbol is valid from its insertion position until the next articulation starts.
I think I'll stick to this solution for now as I have no other at this point.
Hope this helps.
-Vlad