This isnt an answer
I have this same issue except its only on the left track and it doesnt completely fade out it just drops 85-90% and searching the forums im finding no answers for this it started when i got pro on the 2nd update about and hast been right since, I haven't written a single piece of music because of this as my tracks would be destroyed, and for me it doesnt make a difference if i am using their instruments or a vst or vsti im trying to find a free balance knob plugin to put on the main channel but this only makes sense if the bug persists which it has, I havent tried to burn a cd and check yet or released anything because im afraid when its fixed my mix will be all shot to H$%l. Im using the same setup ive used for years with studio one artist and it worked fine when i set it up and continues to do so on launch and sometimes even through a practice but usually i get 3-4 minutes practice max and lose the channel. Very frustrating.