Who I have the same questioned this topic

I downloaded "Android Messages (used to be Google Messenger)" on my Samsung Galaxy S8.  It fails to send and receive MMS messages when WIFI is turned on.  Note that Mobile Data is turned on at the same time and functional.  As soon as I turn off WIFI, the pictures/MMS send and receive.  I tested this with Chomp SMS and the default SMS messaging app on the Galaxy S8, and pics/MMS can be sent when WIFI is enabled.  I'm guessing that for the Android Messages app specifically, it keeps trying to push MMS over WiFi... when it should be handing off those MMS pics to Data.  Anyone encounter this problem or know of a solution?