Toronto, 2004. Train of Thought tour. During A Change of Seasons, "But those days are gone," LaBrie was flat and bowed his head in shame. I have bootleg video of the concert so I can rewatch the pain over and over.
In 2014, during Enigma Machine, the band had just come back from a break in touring so Toronto was their first show of the North American tour. The band fumbled coming back into the song after Mangini's drum solo. It was pretty subtle though. It you weren't familiar with the song, you wouldn't have noticed it. But the band was looking at each other as they got themselves back into the song.
Saw Myung lose it on his stage tech for unknown reasons during a show I think in 2008? Systematic Chaos, I think? Damned if I remember. Been to too many shows.