Exactly what happened for me. Sleep had stopped working MoUsoCoreWorker.exe not showing. Despite being very sceptical followed @SonyVG suggestion of pausing updates then rebooted and resumed updates and MoUsoCoreWorker.exe showed up again, then update offered me KB6401554.That was yesterday since then PC is sleeping properly again.
I guess this will be a reoccurrence every few months then. What a mess-up Microsoft hang your head in shame.
Thank you @Kalaglow I followed the same steps you mention and that same update KB6401554 showed up and installed I am restarting after the update and I'll see if that resolves the issue like it did for you. Microsoft has a mess with their updates every month they screw something up.