I know that the sidebar widgets lose their padding when the Content Layout is set to “One Container”, but if I change the sidebar widget background color in the customiser to anything other than default (#ffffff), even #fff, the padding re-appears.
This is a current workaround – if you don’t change the color but change the padding to something other than the default 40, it will work. There’s a bug currently where it won’t show in the live preview, but the setting will work otherwise.
I’m working on a better method for a future version.