Offline servicing : install servicing stack update first
When scheduling offline updates to OS images, make sure SCCM install the Servicing Stack Update before the Cumulative Update (or allow the users to determine which update has to be installed first).
For example, I had an issue when trying to install SSU KB4498947 and CU KB4494440. SCCM tried to apply the CU before its prerequisite SSU, resulting in the CU being absent from the image.
And the worst thing is that I cannot create another schedule for this CU as it is now missing from the list of available updates. As if SCCM permanently consider this CU as non applicable for this image.