[Kindle Fire HDX 7" & 8.9" Original Android Develop] brainwash123:
Thank you for jumping in.

In the link (don't want to overflow the thread) are the Wifi settings as well as developer settings:

Please note that I've enabled advanced WiFi debugging (yesterday) that shows the RSSID and other details. Also yesterday the "Switch to cellular data automatically" was enabled, just to see if it makes any difference. It doesn't.

I will leave the tablet on standby for a few hours and see when the loss of WiFi happens and will report back.

EDIT:

This may be more than you bargained for, but attached are the logs filtered by 'wifi|supplicant|connectivity|airplane'.

Here are the timestamps corresponding to my actions. After the tablet was sitting idle, it got disconnected, I opened the WiFi panel and the 'enable wifi' toggle was set to off. I keep trying to set it to on but nothing happens. Finally, at 20:43:45, I set the toggle off then on again, which restores connectivity.

09-13 20:37:54.016 1476 2611 D WifiService: setWifiEnabled: true pid=4125, uid=1000
09-13 20:38:33.521 1476 1759 D WifiService: setWifiEnabled: true pid=4125, uid=1000
09-13 20:39:03.717 1476 2610 D WifiService: setWifiEnabled: true pid=4125, uid=1000
09-13 20:40:29.858 1476 6136 D WifiService: setWifiEnabled: true pid=4125, uid=1000
09-13 20:41:35.046 1476 1514 D WifiService: setWifiEnabled: true pid=4125, uid=1000
09-13 20:43:30.257 1476 2212 D WifiService: setWifiEnabled: true pid=4125, uid=1000
09-13 20:43:45.333 1476 5391 D WifiService: setWifiEnabled: false pid=4125, uid=1000
09-13 20:43:49.706 1476 5390 D WifiService: setWifiEnabled: true pid=4125, uid=1000

It seems that the tablet got disconnected at 20:10:35, a few minutes after I pressed the power button to put it into standby

09-13 20:10:35.156 1476 1476 I ActivityManager: Killing 11869:com.google.android.play.games/u0a95 (adj 904): empty #1709-13 20:10:35.288 1476 5441 D ConnectivityService: ConnectivityService NetworkRequestInfo binderDied(NetworkRequest [ LISTEN id=44, [ Capabilities: INTERNET&NOT_RESTRICTED&TRUSTED&FOREGROUND] ], android.os.BinderProxy@c97d75f)
09-13 20:10:35.288 1476 1618 E ConnectivityService: RemoteException caught trying to send a callback msg for NetworkRequest [ LISTEN id=44, [ Capabilities: INTERNET&NOT_RESTRICTED&TRUSTED&FOREGROUND] ]
09-13 20:10:35.300 2203 2203 I wpa_supplicant: wlan0: CTRL-EVENT-DISCONNECTED bssid=aa:bb:aa:bb:aa:bb reason=3 locally_generated=1
09-13 20:10:35.323 2203 2203 E wpa_supplicant: wpa_driver_nl80211_driver_cmd: failed to issue private commands
09-13 20:10:35.324 1476 1618 D ConnectivityService: NetworkAgentInfo [WIFI () - 101] EVENT_NETWORK_INFO_CHANGED, going from CONNECTED to DISCONNECTED
09-13 20:10:35.324 1476 1618 D ConnectivityService: NetworkAgentInfo [WIFI () - 101] got DISCONNECTED, was satisfying 13
09-13 20:10:35.341 2203 2203 E wpa_supplicant: wpa_driver_nl80211_driver_cmd: failed to issue private commands
09-13 20:10:35.358 1906 2792 W Settings: Setting airplane_mode_on has moved from android.provider.Settings.System to android.provider.Settings.Global, returning read-only value.
09-13 20:10:35.544 1476 1618 D ConnectivityService: Sending DISCONNECTED broadcast for type 1 NetworkAgentInfo [WIFI () - 101] isDefaultNetwork=true

The tablet was put into standby at 19:54:40 and woken up at 20:37:23. So WiFi was lost after almost exactly 14 minutes of sleep.