Really?
I'm far from an expert on ball pythons - I have only one. But - he regularly soaks and there has never been a mite on him.
In fact, despite having about 60% humidity in his tub, he regularly soaks before a shed and has never had a bad shed.
From reading the forum and others, and comparing notes with other keepers, it appears that this is not unusual.
I've been told woma pythons never soak. 1 out of my 3 does. One of my two Stimsons does. I could go on but the point is that individual snakes have individual preferences. Some will soak. Some won't.
So if the OP can't find mites, the humidity is correct and the temperature gradient is right - he probably has an animal that just enjoys a good soak.
It's not uncommon..........