Attention, fellow Windows Insiders!
If you're finding that Build 15031 seems to be hung with its Windows Update stuck on "initializing updates" forever, here's the cure:-
Go into Control Panel > Administrative Tools > Computer Management > Services. Scroll down to Windows Update. Right-click that line, and choose Properties from the little menu. Look to make sure that it is set to Automatic. Mine wasn't. It was set on Manual, but it should be in Automatic. Stop the service, change it into Automatic, and then restart the service. Click Apply and then OK, and you're done. Your new Build 15046 should download OK. Mine did. I'm using it here.