Q.trumpet vine losing its bark
Why is my 40 ft. tall trumpet vine losing its bark? It has never done this to the extent it is shedding this year!

I am pretty sure that the peeling bark you are observing is the nature of the beast. Older woody stems are described as stiff with peeling bark (reminiscent of a grapevine) with the younger stems being smooth and flexible.
For more information on trumpet vines, please visit the following link:
https://www.gardeningknowhow.com/ornamental/vines/trumpet-vine/growing-trumpet-vines.htm