I don't think these upsets ever happen when we expect them regarding Clemson, will probably fall short of happening again.
A stark contrast from the earlier years of my college football life, when my friends and I used "Clemsoning" as a verb with very real meaning. "#19 Clemson upset 20-17 by [insert 3-5 team] just before program took the step up to being big time" was a yearly tradition, it seemed.
Came very close to losing against both A&M and Syracuse, with half of the schedule to go. Just give it time, it'll happen. If I had to pick a spot, somewhere in their last three games (a decent BC team, a very good Duke, and a rivalry game with SC) seems like the most likely slipup.