I had a similar issue, problem was a problematic WiFi-router. I got clued in when other devices were having sporadic disconnects once in a blue moon. Turned out that (unlike the brother) they also lost connection but managed to usually auto-reconnect on their own, hiding the issue. After replacing the problematic router all my issues went away.
Not that it'll solve your issue with any guarantee, but if you haven't looked into it yet... .