It sounds to me like his feet are getting trimmed too short. It's just like if you trim a fingernail too short and your finger is sensitive. Eventually it feels better but right after it's inflamed and sore.
Maybe you could give him a supplement that helps strengthen horses hooves cause if you soak his feet to much it will dry up your horses feet and weaken the hoof wall ''NAF'' is a really good brand for supplements😀
Maybe you want to keep your horse barefoot but some horses don’t deal well with having them barefoot because they get so tender. Have you maybe considered shoeing your horse it may be expensive but it sounds like this horse has quite sensitive feet so may require them. I hope this helps!