Actually, the 3 shorter scan attempts using the May v5.48 MSRT all failed, since they skipped the portion of the log indicating the results or infections found information.
This matches what RikDatta has been seeing visually, though we can't tell if all of these failures were for one tool or both, since either the locally installed or downloaded copy all display the same log information within the same monthly copy.
To me the times for the automatic quick scans seem long. but since I have an SSD, the typical time of 1.5 minutes is obviously faster than for an HDD.
It's quite interesting that the June v5.49 tool is apparently operating daily, though I don't know what might be causing this to trigger.
What the above tells me is that at least the copy of the May v5.48 tool logged isn't a file permissions issue, since it initially executes, but fails to perform the scan and probably even open the interface from what's been described.
This now appears to be a suppression of operation issue, though I don't believe that it's lack of Administrator access for the entire account, since this would create many other unrelated problems as well. I'd be looking for anything else indicating problems with initializing programs, which if I recall correctly, RikDatta may have already mentioned relating to tiled (used to be called "Metro") apps earlier in the thread?
This might be aided by looking in the Event Viewer - Application or System logs for errors when these launches are attempted, since any messages found there might help explain the failures more clearly.
Rob
<EDIT> Note that since the failures seem not to allow the visual display of the initial scan selection screen, this could be as simple as an application crash caused by problems with display. Since I believe I recall recently receiving an NVidia driver update for my own older Windows 10 system, there could have been a problem with some systems relating to this update.
This is just a wild guess, but it's the type of issue were looking for that might cause various apps to fail to display and so appear not to operate at all.