shk292:
Could you avoid this by turning the x20s off before resetting the router?
No.
The way it works is that any deco is bound to a network name. Once you factory reset any of the units, it won't know how or who or where to connect to until you tell it either by re-adding it to an existing network or creating a new one. If you factory reset the first deco on the network, that's it you have to start from scratch.