Windows 10 users have been reporting problems connecting to Windows Update since January 29th. Microsoft has confirmed that this was caused by DNS corruption at an external DNS provider that was causing bad records to be pushed to ISP’s DNS servers. Users were able to resolve the problem by switching their DNS servers to Google’s 8.8.8 service of Cloudflare’s 1.1.1 service. Some ISPs cache their DNS data for many days to increase performance, so affected DNS providers kept serving the incorrect information even if the original DNS servers have been fixed.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-confirms-windows-update-problems-were-caused-by-dns-issues/