Dominik_Ecke We have the EXACT same issue (only difference is we are on 2203.)
I have a ticket open with MS right now and all they can say is the issue is related to the CU forcing a double restart (I don't really see it when watching but it does fit) and that the issue is supposedly with the CU itself and NOT SCCM. MS developers are supposedly looking into it right now but no ETA given for a fix.
MS support keeps reminding me in each call that Patching in OSD TS is "supported but not recommended" There workarounds are thus far:
1) Take the patching out of the OSD and let it patch after.
2) Update the WIM file from the MS website monthly so that it included the CU and thus not require during that patching task.
We have grugently set out TS task to patch Win10 only for now and let it patch after the TS completes because updating the TS with an updated WIM file leaves gaps during testing and we have 27 DP (some on slow links) that we'd have to distribute to…
If any new working info comes from my ticket, I'll post it in the comments...