Possible bacterial infection that is causing scale rot as a symptom maybe. I've never dealt with scale rot so I'm not too sure.

Are you washing your hands? You say sanitize, but a little hand sanitizer will not kill enough bacteria to make it safe to handle your snakes. Use hot water and soap and scrub well between each snake.

If you haven't already, change to paper towel.

Double check temps and humidity, maybe they're getting burns.

Trying to cover all bases until you can see the vet.
Good luck!