My wife and I both joined Mint this week. I have been having no problems (Samsung Galaxy S8) but my wife's phone (Huawei Nova 2i) keeps dropping the network and when it is connected only manages EDGE (2G/3G) connectivity, never 4G or LTE. My phone, sitting next to hers, will quite happily be connected to 4G. She also seems to have no connection at all in places where my phone is fine. We were both with the same provider previously with no issues so it's very odd.
Any suggestions? At this stage it's looking like a refund request for one of us at least.