Happy to help
I am glad you got rid of the unwanted categories. That's the kind of thing that will drive one mad...
Re: your sorting question. Are you trying to sort just one category by subject and leave the rest in whatever sort you normally use? I don't normally do that and don't see a way to, given that the sort by function applies to all tasks regardless of what filter you have in place. I can successfully sort by category, then subject; which gives me tasks sorted by subject within each category. I can also sort by subject, giving me one big list of sorted tasks with varying categories.
Or maybe I have totally misunderstood your question all together. Let me know