This is my exact problem, everything was fine till I did the latest update on my galaxy s9 and the only way I can stop it is to restart my phone. I paid $700 for this phone why is it doing this??
Go to Settings, scroll down to Generak Management, select Reset and then Reset Network Settings. Then reboot. I need to do that everytime I get a Samsung update in order to send or receive MMS.
I am having the same issue on my S9+. It will sometimes work if I reset the network settings but not every time. It is getting a little annoying having to rest my bluetooth and wi-fi multiple times each week just to be able to reply to our family chats.
I'm having the exact same issue. Seems to occur randomly throughout the day. I have to restart my phone to get messages to send. Sometimes I have to restart multiple times. Google messaging app gives no issues but I need to use Samsung messaging for Gear watch. Any fixes that actually work?