Hello William,
Thanks for your posting on Q&A.
In order to help me research further, please help to confirm the following:
Did all the updates or the specified updates couldn't import to WSUS console? You want to import 2021-03 Cumulative Update for Windows 10 Version 20H2 for x64-based Systems (KB5001567). Right? I test it in my lab and it worked successfully.
Reference picture:
Please refer to the below picture to import updates on the WSUS console manually:
Then you have to install the Microsoft Update Catalog software on the WSUS Server and import the specified updates subsequently.
Please feel free to inform me if there are any updates about this issue.
Thanks for your time and have a nice day.
Regards,
Rita
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