This exact thing happen to me and what I finally had to end up doing was to factory data rest my phone and it stopped. So try that, if it continued!
Thanks for sharing that, maximbrit, so, a factory reset, I've found, will work temporarily. But it is oh so temporary, very, very short lived. Though I suppose each device could, in all reality, have their various quirks. Last I checked, our phones aren't exactly winning popularity points, as it is difficult to find the same range of information with the ZTE as with other more mainstream brands.
However, keep this in mind, don't forget this, you'll thank me later, I think. I had become so frustrated w my phone's behavior because it was still so new, it still is rather new. I began researching custom, non-stock mms apps and found an article that listed several of the most recommended, reliable mms apps for 2016 or 17. Either the first or second I read about was an app called Textra, available in Google play. I downloaded, installed, set as default and have not looked back. I began w the free version w ads and quickly paid 2 or 3 bucks to have full version, no ads.
To be fully forthcoming, I did receive, two weeks ago, a couple of those notifications again. I posted this information in Textra's forum. Within 2-3 hours, I was contacted by Textra to assist me in finding a resolution. It didn't take 5 minutes to resolve and was nothing more than a setting within the Textra's app that dictates size of mms incoming/outgoing.
Their customer service is amazing in contact, resolution and in follow up. If your phone continues on, I say check out Textra. Its a nice change of pace from the same ol' boring stock! And for a couple bucks, no ads.
