New
#21
I've found that if WU doesn't do the job for Defender updates, you can often update from inside the Virus Protection portion of the Windows Defender Security Center. If you click on "Protection updates" you'll get to a screen where you can click to download updates. Even when WU balks, this function often works for me. Hope it does likewise for you.
HTH,
--Ed--
PS: if that doesn't work, I'd recommend trying the Windows Update MiniTool (WUMT) next. You can download it from MajorGeeks.com.