Want to chime in that I have the same issue and first identified it in the first day I owned mine because I was moving files from my network share to my new SP7.
Every time I use it I have to disconnect wifi, wait a few seconds, then reconnect to my Ubiquiti/Unifi brand network. I still think on occasion its slowing down while in use.
Anyway, if I don't do the above procedure I am stuck at around 15megabits/sec on my 480 megabit connection line of sight to an accesspoint.
I am still in my return period.. I need a real solution before my return period ends or this is going back. I'm not dealing with this for the life of my product.