4 year old toileting woes

Dear mum's/ dad's

I have a 4 year old...
We have been toilet training for a realllllyyy long time. Mostly gently .. meaning.. led by my 4 year old.. We haven't want to push him but as his shown interest encouraged him.

It looked like this...

Started following us to the toilet.. then would ask questions and show inquisitive behaviour of his own bodily parts... Started trying on the potty.. eventually was able to see in potty... then started to see in toilet.. has regular accidents but was able to wee in the potty.. this went on for a long time.. But will never intitate himself if his not reminded every 30 minutes to an hour .. He wets himself he never says oh I need the toilet...

Then we moved to trying to get number 2s in the toilet.. this went on for a long time until we identified .. that he would go and hide behind the couch or in his room, just disappear quietly .. so we made a conscious effort that went he went to hide ... We would ask him if he needed to go.. which he would always say no.. so we started taking him anyway... eventually he pooped in the toilet for the first time and we used a sticker , money, reward system.. every so many stickers he got money .. He likes money.. and at the end of the chart he gets to spend it how he likes .. his 4 yes but very cluey.. and this was what works..

Anyway for a while we thought we were almost toilet trained despite a good number of accidents, he began saying quick need to poop, would poop get his sticker and off he would go.. But then all of a sudden back to popping his pants.. says he wants to be a baby and just won't use the toilet.. Just wees and poops his pants..

I can't understand how he can hide knowing his going to poop, or go from using the toilet to just flat pooping in his pants.

I don't know what to do we really need to toilet train him.. I should mention he poops several times a day, have had him checked regularly by a peaditrician, he has rather lose stools but doctors just think it's toddler dirrohea and can't find any reason .. have checked dairy intolerance and cealiac etc.. his poop seems to really irrate his bottom, even if a very short time.. It goes very red like sunburn and looks like it may blister .. When he was using the toilet this stopped. It gets so bad he can't walk. He does have kidney and urology issues but have spoken to his team and they said whilst he might be harder to toilet train , that have no advice etc .

I'm not even sure his made the connections or if I'm doubting myself bit feel if he can wee when it suits him and can poop at times in the toilet.. while he isn't trying to go more frequent , I suspect accidents but it seems like his just flat pooping his pants.. with no attempt to make it to the toilet.

Anyways advice or thoughts would be appreciated. I really need to toilet train him.. his in kinder and also off to school next year.