When using the "walk through windows of current application" shortcut it opens the right interface but doesn't cycle through all windows.
Just the one. If I press the same combination again (or reverse) it does nothing
If I'd have to guess, I'd say that it recognizes the windows switcher as current application and it just freezes.
Options:
Using Plasma 5.15.4, I noticed that walking through windows of current application only walks through 2 of them. But backwards cycling does cycle through all windows, so you could use that as the standard key shortcut.