You do not need a fogger for a boa. They are not tropical per se. The fogger, combined with a coir substrate, suggests that the snake is constantly in contact with damp substrate and this will lead to scale rot. The snake needs to have access to dry substrate. From the photos, it does look to be scale rot.
It's easy to treat.
First off, take out the substrate and use something dry. By all means provide a humid hide box filled with moss for example, but the substrate needs to be dry.
You then need to get some povidine-based iodine paint. Every day the damaged scales need to be painted. At the next shed, the damaged scales will be gone.