I don't know.
but I do know you can get a few bubbles and even some wheezing if a snake has been underwater or if I give a snake a swim in the bath. A bit like us if we go swimming and go under the water.
if the bubbles and wheezing continue then be concerned.
You said no mites. So Soaking can just mean they want to shed or support their body weight after feeding or cool, or many other things.
No disrespect for your knowledge, I do not know that, but Also are you sure its a he? females soak or bowl wrap during follicle development.
regarding the hides, if he cant fit into them anymore then maybe a bigger one is needed, but they like it tight.