Hi Gelly, I've seen your latest threads and your setup and I think it can be related to stress maybe visiting vets and all medications etc, it can be sort of depression or something. I also think your setup is very strict and more like display setup, maybe he doesn't feel safe and private there, maybe I am wrong just got this impression.
What I would do I would probably get a smaller crate like a travel crate just size of a litterbox so all his floor is his litterbox, absorbing layer (wood or recycled paper pellets) underneath and a good layer of hay on top, I know he also had sore hocks so I would go with recycled paper pellets they are softer, or mix wood pellets with shavings, hay n top as well. I wouldn't use any training pads I see now in there.
So I would make this cosy little place for him just like his toilet size full of soft hay and covered with a blanket from top and 3 sides so only one side front is open, also can be half covered so he can feel privacy. I would let him be in there for a week only opening door for an hour same time every day if he wants to go out, if not I wouldn't force him, just leave the door open and close after one hour.
Then you just leave him in there only coming twice a day morning and evening to feed and top up his hay, change water, just say hi and smile and go away.
With proper setup of his toilet pellets underneath and hay on top you will need to change his toilet once a week, if you see it is soiled sooner then after 3-4 days. don't worry he will be fine, just leave him be and you will see in a couple days how it goes, maybe he had too much attention with all his health visits and also can feel your panic.
I find that leaving them like I described makes them feel safer when they get that no one is approaching them in their safe place so they can relax better.
Also sore hocks should go away during that week without any medication since he will be on soft hay all the time and there's absorbing layer underneath so he will stay dry all the time.
After one or two weeks of staying in this covered safe toilet you will want to rethink your setup and he will get more attached to his cosy toilet maybe now it is not attractive enough to him.