Others, on answers.microsoft.com, like me, are presented with sa.*_5_.Public.AppUpdate.dat files in C:\Users\*\AppData\Local\Temp since Windows 10 Fall Creators Update was installed - December 6th in my case. No useful answers were forthcoming. The total number of such files each day totals forty, approximately, which I delete. I have not checked to see, yet, whether those appearing the next day are the same, or different files.
Update: some of the file names are the same. There were forty-eight yesterday, however, compared with forty today. All arrive at one time: yesterday at 13:48, today at 11:13. .tmp files such as SAS8850.tmp arrive, too, with historic dates such as 20/07/2017.
Edited by lithoartist, 15 December 2017 - 12:46 PM.