Yes, happened to me. Once Xcode 8 just crashed and exited, and once it took down the entire machine, hang first and then auto reboot.
What I noticed before those two crashes was that my keyboard input seemed to “hang”, e.g. I’d type a line normally and when hitting Enter, the cursor stopped blinking and everything just stuck. I could still move the mouse and click/type around vividly outside of Xcode, but in Xcode everything was idle, at least 10-20 seconds in one go. When it eventually came back, it was looping my input, like I had kept pressing the Enter key over the entire time it idled.
This happened two or three times, maybe 30 minutes or an hour apart, then Xcode crashed.
However, it’s not crashing on a daily basis here, only twice so far.
I don’t see a pattern yet. But yes, it seems to be related to the syntax checker/highlighter.