I've seen several heroes come unstuck for various reasons.
James Brown at Hammersmith Odeon, in the 80's. During his "drugs" period. Very untogether, even the band was off.
Little Feat, the Craig Fuller line up. They started with a great balance. Sounded like a record, and got progressively worse during the night. The FOH sound guy was shambolic.
Robert Cray at the Shepherds Bush Empire, about 10 years ago. It was music by numbers. Very bland, they were just going through the motions.