Just from a slightly differnt angle I've heard Ralph McTells performance being slagged-off 'cos he didn't sing "Streets of London", and van Morrison 'cos he didn't sing Brown eyed girl.
Can't think of anymore examples, but I would expect a top liner at a Fest to be able repeat one or two songs in a 2 x 45 minute sets especially at different locations within a very tight time frame at the same Fest.
At the Final concerts (2 run sinmultaneously) at Saltburn , Garbutt is 1st performer at one concert, and final performer at the other.
Both concerts will be full - so I don't see the problem of repeating a song if it went down well in the first concert.