I haven't exhaustively tested it, but I think I've narrowed it down to what causes this bug. You know when you head to your performance location, the job panel pops up in the left hand corner giving you the address, performance time and what you need to do to complete the job. Well it seems for singing performances (and I assume for magicians and acrobats), if you go to the location really early, then that panel seems to disappear after a bit, and if I start my performance whilst its not there I get bugged. I was heading to the venue first thing in the morning and then performing for tips until the show was about to start, which I guess was causing one of the script triggers not to activate.
If I wait until a couple of hours before the performance is due to start and only then head to the venue, the job panel pops up and everything is fine (so far at least).