Bonded cats are fighting - help!

Okay so, my 6 year old ragdoll was profusely dribbling on Sunday night, and it was quite worrying, so it resulted in a vet trip on Monday. We were in there for 40mins tops. She was given the all clear, and no treatment was provided.

Brought her home and everything was fine, until the evening when my 10 year old cat started hissing at her, which resulted in a fight.

Now, I’m very aware the vet smell has thrown him off from knowing who she is, and they’ve been separated ever since. I’ve been using clothes on them both so their scents get back together, and leaving blankets/beds and clothing with each other so they get reused to the scent.

Today, as I’ve been home all day, I’ve tried to slowly get them back to knowing each other presence. Was positive, with them eating dreamies in the same room together but 10year old is still hissing, then running back to hide under the bed. They got relatively close and ragdoll ran at him after he hissed again. She wasn’t hissing, tail wasn’t puffed up. It was as if she wanted to play.

Separated them again, until she got comfy and then I opened the living room door. 10 year old took his time but he came down and slowly came in the living room, and just as he looked like he was going to jump on me, she ran at him again. This resulted in a chase upstairs, hissing, a bit of fur and both cats hiding under separate beds.

I’m at a loss. What is happening and what on earth can I do to get them rebonded?! He’s known her since she was a kitten, and they’re very well bonded and this is worrying me massively!!