Sorry I haven't read through all the replies.
Have you tried talking to him during the day about what his issues are? My 5 yr old is better at talking about things when it's not happening right in front of him iykwim.
We seem to go through cycles of someone not sleeping in our house and what works the best is to reset and crack down on the bedtime routine.
I recently did some reading about worms as my boys are always hungry 😏 (apparently hunger isn't a symptom lol) and apparently sleep can be affected a lot by those little buggers..
Good Luck I hope you get it a sorted