num_selections used to be 0 when you had only a single cursor and no selection. Now it doesn’t match against anything if you don’t have a selection.
In other words, this will never trigger anything:
{ "key": "num_selections", "operator": "equal", "operand": 0 },
Worse, it seems that if you have multiple cursors (but no selections), then num_selections is still an unknown, unmatchable value. So it’s impossible to check in the key bindings whether there are multiple cursors. Can we get a num_cursors key to check for?