What I was thinking caused the backlog is that they may be focusing on all those applications that they promised to complete by December 2017 and were supposed to take years, like you said. There may be quite a bit.
I think they give you a deadline for the sake of it, since people that submitted it in April haven't heard any follow up on it. They will probably process it together with the rest of your application. I'm not quite sure why now they ask to submit that and police certificate after they receive the application since they still take a long time to look at it.
I don't think so
Like I said earlier April applicants are still waiting for medical request with no SA at all. They haven't heard anything after submitting Schedule A and PCC