KM freezes in Catalina 10.15.7, but oddly enough only here:
1.- Open KM 9.1
2.- Make sure KM is not in Edit mode
3.- Do a search in KM 9.1 for something like "math"
4.- Select a disabled item from the results (I selected the Napkin macro, which is inside a "Work in Progress" folder)
5.- Close KM using CMD-W
Result: KM freezes, have to force quit
Have not checked thoroughly with other macros, but oddly enough happens only with this macro
Hmm. I followed your steps but made sure I selected All Macros from Groups first so the search would be comprehensive. I have two inactive Napkin versions (one for the hotkey mod and the other for the Markdown version) and one active. They were in the results list.
I selected each of them and they each came up.
Then I hit ⌘W and the window closed.
So I can't duplicate on Mojave (10.14.6) the problem you're experiencing. If it helps chase that down, "math" appears in the Draw mode HTML form.