2 years ago I bought 2 M4R decos to use as a wifi mesh, I disconnected my ISP wifi to keep it without any interference and connected both decos to the ISP router by cable.

For the last couple of months the mesh signal keeps dropping abruptly, but both decos light keep a steady white (all is ok), after a time which can be a few seconds to several minutes the signal returns. 

This happens to the phone, the smart TV or the tablet. I even had to turn the ISP wifi back on to use wifi. Both decos are updated and had been restarted manually and via app several times.

Does anyone have any idea that will help?