If you have an ATT phone that might be the issue. I recently switched from Verizon to ATT (I was moving from iphone to a Samsung Note 4, so figured why not switch carrier too). ATT does allow, with effort and searching, you to shut off auto connect to mobile hotspots named ATT (security issue, clearly). But has disabled the ability to not show notifications for wifi connections.
The bottom (second) photo I attached was from my ATT Samsung, notice the top wifi box is unchecked. Yet, if I was sitting in McD playing a game, constantly the white box with connecting to xxx network would pop up. It was so annoying that I would turn off wi-fi. Then forget to turn it back on later, and use more of my data plan. My best guess is that is why ATT does this. I chuckled when I looked at "old" ATT (bottomphoto) screen because you can see I had airplane mode on - that was to stop the wifi pop-up insanity!
The top photo is my new Verizon, whom I switched back to a week ago. Notice the connection says "or connected"? This is what ATT removed that caused issues on my phone.
If you don't have ATT as your carrier, than I don't know what the issue is, however, for me switching from ATT to Verizon solved this annoying design feature.
I hope this is helpful to you. The pop ups were driving me crazy while I was playing games!
