Dealing with devit
Yes this sounds like the most usual form of devitrification.
The best way to deal with it is to prevent it. Very good cleaning without additives and polishing dry are the best ways of preventing it.
In firing you need to go quickly through the devit range ca. 670C to 750C both up and down.
Abrasion of the surface whether with sandpaper or sandblasting will deal with the devit, but leave fine scratches. These can be removed by firing to fire polishing temperatures. You will need to go slower on the heat up than originally. Once you are about 50C above the annealing temp, you can go fast to the fire polish with only a very, very short soak, then down to anneal soak and cool.
Another way to deal with the devit is to apply a devit solution, such as borax or one of the branded products take the piece to fire polish and anneal.