The notion of an explanatory 'gap' suggests that something about consciousness has already been explained satisfactorily. What is that, I wonder?

The notion of a gap is also potentially misleading since it implies that the method being used is OK but that it can't quite get us to the target - or can't just yet.  But the fact that something cannot be explained by a certain method may also mean that the method is completely inappropriate to the task.  Then we are not talking about a 'gap' but a kind of abyss - or, to change the metaphor, a philosophical dead end.

The term 'gap', in other words, betrays a certain philosophical complacency, does it not?