It started this morning (Wednesday, 6/11/14). I have sent and received MMS messages seamlessly until about 8:00 this morning. Now, if I am connected to a wifi network, but do also have data enabled, I cannot send or receive MMS messages. When sending, it just hangs and doesn't send until I disable wifi. When receiving, I get a message wanting me to click "download", but when I do, nothing happens. Turning off wifi makes both messages go through immediately.
I understand that MMS messages do not go through wifi, but, as I said, until this morning they could go over the data network as needed even when I was connected to a wifi network. The change was sudden, and I'm not aware of anything that changed with my wifi connection or my phone, though my apps do typically auto-update, and I don't know which, if any, may have auto-updated this morning.
Sorry to hear about any trouble with your picture messages! Let's get everything back up and running for you. Is mobile data still turned on when you're connected to WiFi? If so, can you try using the Google Hangouts application for your messaging instead? I'd like to test if this will allow you to receive picture messages even when on WiFi. Keep us posted!