Having heard about the antics of your lot, it’s anyone’s guess what their reasons are. They’ve probably got an underground tunnel connecting the bungalows and the nesting material moving is just cover.
But maybe they thought it might be a good idea to insulate from the heat outside? The females do go out in the day sometimes when it’s hot to get some peace from the hoglets, but it seems a bit extreme rearranging the nest next door when it’s that hot. Don’t think I’ll ever be able to get into the mind of a hedgehog. I sometimes think they just like to keep us all guessing!
But, seriously, it’s good you’ve got tenants for both your bungalows. Hope that hoglets, or prospective hoglets fitted in somewhere in the scenario.