When Giancarlo gets into the shower on stage, he gives his towel to a stage hand. When he gets out after his aria, the towel is around his waist. There is a brief moment when the camera is on the audience and not on him, but hardly enough for the stage hand to come on stage, hand over the towel and disappear off stage again.
The goof item below may give away important plot points.
Monica receives a call on her cell phone and she is offered a part in a movie that will take her to California and then Japan. As the scene is actually taking place in John's memory, some 30 years in the past (circa the early to mid-1980's), Monica could not have had a cell phone, but must have received the news some other way. Cellular phones of the kind shown were not in use in Europe prior to 1993 at the earliest.