Android 7.1.2 drops WiFi connection. Wi-Fi verbose log says:
I found out, the following WiFi Manager App was the reason:
Wi-Fi Privacy Police (Prevent leaking sensitive data on WiFi)
The problem disappears whenever I disable this app. Here is how to disable it:
(System) Settings / Memory / Apps started on boot / Wi-Fi Privacy Police / Start at boot: DISABLED
So you disabled the App's bootup autostart. Now reboot Android. After you have Android rebooted, check again Android's Wi-Fi settings: The error message NETWORK SELECTION DISABLED BY WIFI MANAGER should have disappeared.
Wi-Fi Privacy Police was actually a useful app for long time, till I noticed the unfortunate repeated interrupted WiFi connection. Below you have a screenshot of that app's functionality: