RT-AC87U ........ have you tried a different router for testing the problem?
Are you aware that there have been major issues with this router ?
The Quantenna WiFi drivers are terribly unreliable and the router design adds to the problem by getting too hot.
The processors have no heat sinks, they are pasted to the plastic shell and when you have a lot of clients and traffic they get extremely hot.
The excess heat kills WiFi and over time damages the main CPU.
Many people have added cooling fans, or use a laptop cooler to stand the router on, that reduces temp by @ 50%.
I have had 4 of these routers , every one was faulty and got replaced by the supplier, in the end they withdrew the 87U and I was offered the AC3200 as a replacement.
Just a thought, your issues could be due to the router ........
: Synch : 80/20 : Grade A : Download 75.31.Mb/s : Upload 18.71 Mb/s : ping 10 ms