My advice would be to back off completely for now. Totally ignore all toileting and go back to nappies full time. He needs to be comfortable about releasing wee and poo. He sounds like he is constipated too because a little bit of runny poo escaping often happens with constipation (it comes down around the compaction).

After a few weeks I would gently encourage a discussion around toileting, but try not to put expectations on him...he sounds like it's become sensitive and he's ashamed of it. I would also openly show him his wee and poo in his nappy in a really positive way...talk about digestion and food and how interesting and wonderful poo and wee is.

You need to banish all negativity so he can feel free to eliminate without shame. I think that's why he is holding it in.

Good luck