I noticed the same thing on Thursday when I was in the area. A few weeks ago I was able to get an LTE signal getting gas at Costco but when I went back this week I didn't have one. My phone did switch over to LTE in the middle of Eden Prairie mall, which I found odd. I did however get a strong signal when I was in Chanhassen yesterday.
I wondered if they were blocking it to but why would they only block it in EP?