So I converted the Stargazer Lounge penthouse lot in San Myshuno to a residential lot, using the Uptown Glass lot that shipped with CL. (I moved Judith Ward there so I could use her lot for my Arts an...
I had the same problem. I replaced The Solar Flare lot with a residential lot, but my sims still had events there. I renamed the lot, deleted it and put it back, restarted the game, etc, but the event was still there. I just ended up ignoring it and the next showcase was somewhere else.