I decided to try scannow and it gets to 34% and then stops with the error message "Windows Resource Protection could not perform the requested operation." The internet shows a way to fix this but it is complicated and I may have made a mistake because it did not work.
I think Microsoft is getting too cute with added complexity that will make most people have problems.
As I mentioned with the last build, I'm not overly concerned with this issue as I can remember back a version or two of Windows 10 have had this problem during their Insider runs.
Mine failed like yours and then after a couple days of running that build I did a system cleanup and tried again and for some reason it worked the second time.
Haven't tried it yet with this release.
Interesting thought, no doubt a possibility worth considering.
ON the other-hand I prefer to think that sometimes it works and sometimes it doesn't....
That's the new "Microsoft Normal", the only thing reliable is its' unreliablility