If you don't have enough signal, the MMS will not download. I would recommend contacting your carrier to check your APN settings or see about getting a replacement SIM card.
The message isn't downloading at all, or do you have to touch the message to download it? There's a setting that you can turn on in Google Messages called "auto download MMS when roaming". Go into the app settings, and then the advanced settings and you should see it. That will have it automatically download it when you're roaming. Not sure if that's what you were asking. Hope it helps!
Not sure why they would say that, but for me, I switched to the tmobile sim and was able to get utilize tmobiles 5g network. The tmobile employee that helped me when I went in to get the sim card, said that Sprint phones were not accessing tmobiles 5g network, even though it shows you're on 5g. After the sim was put in, my data speeds increased dramatically...
