Every once in a while, my Galaxy s10 has trouble downloading and sending group messages. For about 30 minutes or so, all incoming messages give a loading circle and just say "Downloading", and any messages being sent fail. Service is fine and happens on both Wifi and 4G. This usually resolves itself eventually, but is frustrating when it happens. Any help on this matter would be appreciated. On Verizon using the Samsung Messages app.
So here is something you can try if you haven't yet.
Go to Settings > Connections > Mobile Networks or More Connection Settings > Check to see if VoLTE is ON. This setting allows your device to be on a call and receive mms messages or access the internet at the same time.
You can also try to clear app cache/date, etc..
Hope this bit of info helps in any way.