Hi,
once it detects the primary SDWAN connection is offline it fails over to the Cellular carrier.--- this can be seen from the default route next-hop change .
If the SDWAN comes online, is the next-hop changing back ? If it changes back ,I think there is no probelm in this .
However the ping test out the SDWAN interface continues to use the cellular next-hop.--- This , I think is according to the current routing table for the given target (destiantion) .