I have a wifi watchdog installed because my wifi connection sometimes breaks off.
It automatically turn the wifi controller off and on again, when the pi can’t ping my router. Maybe u should check this out:
http://alexba.in/blog/2015/01/14/automatically-reconnecting-wifi-on-a-raspberrypi/
I just replaced the used IP Adresse from this Tutorial with my routers IP adress.
Brainstorming again. Maybe your Pi doesnt have enough power for the wifi controller when u turn on your alexa, magicmirror and such other stuff.
So it cannot hold the connection with the -71db. Maybe a repeater would help, so with e.g. -49db the wifi Controller doesnt need too much power