The steroid doesn’t contain an antibiotic, so won’t be a problem – but the new rules mean that any antibiotic needs to be prescribed at the point of seeing the patient. This part of the rules has come into force at the beginning of September.
It might be worth talking to the vets and seeing if there is a different medication that doesn’t contain a restricted antimicrobial that could be used instead?

If you’ve followed all the steps, maybe consider talking to a clinical animal behaviourist?

Definitely have a chat with the vets – try to find out WHY they’re asking you to withold food; and if more tests are needed to find out what’s going on rather than repeating the same cycle.

I’d be really concerned about this from animal welfare grounds, let alone human health ones…

I’m so sorry to hear that!
I would say that there clearly IS a reason – we just have no idea what it is. Have you considered referral to a tertiary referral specialist, as a last attempt to get to the bottom of it?

It does sound like there might be some cognitive decline, although other medical issues like kidney disease are also a possibility – I think time for a thorough check up at the vets, and see if there’s a simple medical cause, and then take it from there. Good luck.

Right, definitely vet time!

It’s uncommon, but usually it’s because they’ve not been able to access all of the reproductive tract through the flank incision, so have needed to extend. This can happen if the cat is pregnant (although I’d expect them to have told you about that), or there is a technical problem, or the anatomy isn’t quite textbook (remarkably common!).

I think from what you’ve said, you need all the information you can get… Definitely check for Addisons, that’s a good shout, but you might need to think about scoping and even gut biopsies to get to the bottom of it.

Unfortunately, I think you know the answer – this does sound like irreconcilable differences, as it sounds like you’ve done everything pretty much right.
The only option I can think of at this point would be a consultation with a good clinical animal behaviourist, who might come up with some fresh ideas – good luck!