Every year I receive calls regarding trees in which the bark sheds for no apparent reason. This understandably creates great alarm among growers. I see it most often on Desirable but it can occur on other cultivars as well. Usually the outer bark layer sloughs off exposing the inner bark layer, which has a brown or cinammon color. As long as you don’t see the light yellowish/white wood underneath the bark and the tree is showing no other signs of problems, the tree is fine. Here are a few photos I have received this year of this problem:
See this 2015 post covering the same topic for more info
Bottom line here is don’t panic, the tree is just doing its thing.