Unable to do system restore at boot after Ntfs error

About an hour after the automatic installation of Windows Update KB2919442 (Windows 8.1) on April 1, I began to get Event 55 errors showing up in Event Viewer (screenshot attached). I tried to go back to the System Restore point before the update, but the restore failed. I ran sfc /scannow and it found corrupted files but could not fix them. I ran Dism /Online /Cleanup-Image /RestoreHealth and it found and fixed corruptions. I then ran sfc /scannow and it found and fixed corrupted files.

And the same error message recurred in Event Viewer about an hour later. I ran a full Windows Defender scan and Malwarebytes (free version) scan and nothing was found. Chkdsk is OK. I then tried to go back to several different System Restore points at boot, logged in as the BIA, and all attempts to restore failed. I then tried to run sfc /scannow from the command prompt at boot, but got the message "an error repair is pending". I let Windows load, waited a while, rebooted, and tried the command prompt at boot again, and got the same message about a pending repair. When I run sfc /scannow from within Windows, it says everything is healthy. I chatted with Microsoft support, and they said Event Viewer sometimes gives false alarms. My PC seems to be fine if I ignore the facts that I'm getting Ntfs error messages every couple of hours, System Restore doesn't work, and I can't use command prompt at boot...

Am I looking at spending tomorrow doing a clean reinstall, or is there some way I can fix this?

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