They sound like some very stubborn mites, my Starsky was litterally covered in mites when I collected him from the pound as a rescue, so much so that you could see them moving in black waves over his skin when ever I went near him and put a hand out. The mites would swarm away so it looked like and ocean ebbing and flowing. One dose of revolution wiped them out in 12 hours. Can you see the mites ? Often you can’t as they are so small but if they are there in volume they should be partially visible. What colour are they ? There is another mite that can come in on the hay and it is generally miniscule and red but you pretty much need a microscope to see them. They don’t usually bother the buns but leave us humans covered in welts that can very quickly turn septic.
With the Revolution did you treat both the cat and the rabbit just once or did you repeat the treatment after a few weeks ?

Next question, are you in units or a house ? If it’s units does anyone else around you have pets ? You may be treating your place only to have them invade from elsewhere the minute you are done.

I know Revolution will kill mites and fly larvae in addition to fleas because it is selamectin, not sure with Advantage though as it has another active ingredient which is also bunny safe. Advantage definitely does fleas and some intestinal worms. I have to do some pondering and digging about. Hopefully some one else may have some insight whilst I am doing that.

I would avoid tea tree oil or eucalyptus oil on buns and use either diluted mineral oil or olive oil.