Apologies for the late reply.
So, after a few days of observation and experimenting, I have...absolutely no idea.
Some days he's perfectly normal, and some he's normal and then at one point he reverts, and one day he was on and off.
Yesterday I actually moved his bowl and litter into the...
Ah okay, that sounds simple enough.
I wondered that too, but when I'm in another room I can hear him eating sometimes, and usually if I leave and come back after a little while I can see him eating.
Oddly enough, yesterday when he was again not playing, we decided to take his food bowl away to...