I have the same problem with my new S10. I contacted support and they even remoted into my phone. Couldn’t fix. Blamed it on my carrier. My old Galaxy and same carrier worked fine. New phone did not work day one. Tried everything. Keeps happening. So annoying
Just a shot in the dark, this might not be your issue.
But long press on the messaging app, then go into -app info -mobile data, and then make sure both -allow background data usage and -allow app while data saver is on are both turned on.
I know that when these are off, group text messages come individually in a compressed file that you have to download before it will actually go into the group text.
It might help with your picture files too if you have those settings turned off for any reason.
Not sure, but good luck.
I've had this problem since around September. I have reset my network connections so many times and it does work for a few hours. The only solution is to turn off wifi and download the message and turn it back on, which is fine except when you have no cell service at your house! I also have AT&T. I got a new SIM card tonight hoping that would work and it doesn't! I have had Samsungs notes since the note 3 and AT&T and I've never had problems like this. There is something wrong on Samsung's end.... this doesn't happen with iPhones on AT&T network. Please please PLEASE fix this!
I have AT&T service. I had the same issue and fixed it like this: 1) Go to google play store, select menu, select settings, select auto update apps, select don't auto update apps, restart phone. This fixed my problem that was driving me bonkers for weeks. This does not require turning off Wifi or Wifi calling. Good luck!