FJ had some early hiccups. Gringott's had major downtime early on, but they worked it out. Hagrid's has had more downtime and continuing issues (Intamin?).
Each major Potter attraction has become more complex/cutting edge resulting in more "technical difficulties".
Based on what came before, (FJ, Gringott's, and Hagrid's), I am excited to see what Universal Creative is gonna throw at us, downtimes and all.