I switched from iPhone to Android a few months ago and while I love it, the only issues I've been having are occasionally not receiving messages from iPhone users (which include my entire family, unfortunately). Once we got over the initial problem of not receiving any of their texts if they were in Group messages (by asking them all to delete their previous conversation history with me, as un-registering my number with iMessage didn't help at all), it was mostly going well aside from the occasional missed message. Now out of the blue, I am getting "Could not download message" notifications, and when I go to the particular conversation, I see they tried to send a MMS. It gave me the option to try to download the MMS again, and in all cases after about 5 minutes I again got the notification that it could not be downloaded. This has happened both with pictures and with videos. I was on wifi everytime, with strong signal (in my home or at work). I'm on a Nexus 5X using the default messaging app.