Not sure if anyone else is having this issue but MMS have been a real problem with downloading the messages. It's sporadic but won't download the message more often then it is downloading them.
T-Mobile customer on an S22 Ultra. It happens to me every single time I receive or send any MMS message (group chats too, not just pictures, GIFs, or videos) when Wi-Fi Calling is enabled and in use. Turning off Wi-Fi or Wi-Fi Calling fixes the problem, but I don't have this problem when using Samsung Messages. This happened on Android 12, too.