The segment has since been repaired. An investigation is ongoing, but there aren't any identified culprits as of this writing.

Just why someone would slice off a portion of the road isn't certain. While solar roads are relatively expensive to make, the actual solar panels aren't worth that much. The thieves aren't going to make a fortune, and this wouldn't be enough for personal use -- especially not when there's a layer of transparent concrete on top. The most plausible explanation is that someone wanted to see how the technology worked and, for some reason, couldn't just ask the developers.

This probably won't be an ongoing problem. However, it's reasonable to say that this isn't a significant issue for ordinary roads. So long as solar roads remain novelties, there are bound to be people curious about how they work. It's just a matter of whether or not someone let that curiosity get the best of them.