Hi, @arnaud essers
Thank you for posting in Microsoft Q&A forum.
For error code 80244007, this issue occurs when the number of updates to be synchronized exceeds the maximum number of installed prerequisites that a WSUS client can pass to SyncUpdates.
You might have checked below article, after change the web.config from 400 to 800, did you run IISReset? Does the solution work for you?
https://learn.microsoft.com/en-US/troubleshoot/mem/configmgr/error-80244007-when-wsus-client-scans-updates
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