im mostly late to this topic but i was experiencing the same thing.it turns out debris consisting of dust and other tiny things where causing the issue .the front dial is not weather sealed and dust gets in there .i had to blast it with contact cleaner and that did the job for me .before it was either not increasing the iso only decreased it or it woul jump backwards randomly when in picture view mode when trying to go back on the viewer. it fixed it for me i thought it was software related or just a bad dial.it turns out it was just dust.
