I don't know what level I am, because I restarted last September after a 56 year gap when before I had scraped a grade 3. But I just learnt "Cool" which is a grade 5 piece (took lots of metronome work to get the rhythm correct, but that's another story). About 2 weeks ago now I started Bach's Invention No 8, and although I very quickly could play it hands separate, I just couldn't play it hands together. I found a set of exercises to help with hand independence which really helped
Hands in C position, play left hand legato, right hand staccato up and down the 5 notes, then swap over. Now repeat with the legato hand going double the speed.
There are more exercises (doing an arpeggio with the staccato hand for instance), but the second exercise above showed me immediately where my weakness was as I could do RH legato (double speed), LH staccato easily, but the other way round (ie LH legato double speed, RH staccato) just wouldn't work. I just concentrated on that exercise for about half an hour and it started to come together.
This was before my teacher had any input. Once I was into the lesson, she gave me some more tips.
1) I was struggling to play the right hand main motif when it starts in C (just after the end of the first section) and she said that it was because my LH wasn't fluent enough in its fingering playing the run down from Middle C to the C below, so I was stopping to think about it. So suggested just practicing that bit in the LH until it was so automatic, that I could concentrate on the RH. EDIT: Just to emphasise this is hands separate practice
2) I was falling apart when I tried to make the RH play the very final part of the first section loud. So she suggested just playing the three or 4 notes around the transition from even to loud in the RH whilst maintaining an even LH. EDIT Hands together practice.
I hope these little ### bits that I have just learn can help