I had this problem since getting the TP link mesh system. My dell laptop would connect (Intel AC 7260 wifi card) to wifi but then not have internet connection. Tried resetting options on card etc. Very frustrating. It would keep trying and then after 3-5minutes would connect and be fine.

I fixed this by going to advanced  -> Address Reservation -> removing the laptop off the address reservation list. I'm no sure if I added this manually in the past. Since removing it off the list, the laptop connects right away.

Hoping this will help others.