I too have an SP7 and a unifi setup (usg P, HD ap and two UAPs, cloudkey and 5 various unifi switches) with zero issues. If you have fast roaming on, switch it off, and i leave
running controller 5.13.9 and devices on 4.2.0.1 and also have band steering off) i have no issues on a 380/3imbps cable connection. I have no issues, so I would look an unifi to make sure its good. I also have DPI and IPS on.