neowin[.]net/news/fix-for-windows-10-failing-to-install-kb4023057-update-because-it-is-already-installed
Not a lot of info yet, it seems to effect version 1803 & older, and the update, kb4023057, was likely already successfully installed in December, 2017. It's reported that Microsoft is finally moving to the normal rollout schedule for the win10 fall update, v. 1809, more aggressively pushing it out to Windows devices via Windows Update. The hotfix, kb4023057, added improvements for update reliability, so perhaps flipping the switch to open the floodgates for the fall update triggered the broken attempts to reinstall kb4023057, but that's just my guess.