Sony xbr-55X800E got the update just a couple months ago now and ever since then the wifi disconnects when the screen is off and I can no longer use the android TV app to wake the TV, also having trouble casting sometimes. Also can't use voice controls from Android TV app on my phone at all since update.
I'm having this same issue on my shield tv from time to time. Just got the 8.0 update I think.
Same problem here with the Philips TV
Same problem (Philips PUS7303/12). I contacted Philips and got a lacklustre response about turning the TV on and off again, disabling and re-enabling all associated settings, etc. etc. No improvement.
The TV settings claim to allow wake-on-WiFi, and wake on Chromecast, but as soon as the TV has been off for more than a few minutes it disconnects.
Try WakeLock v3 - needs to be side loaded (Play Store version doesn’t work on Android TV). Works with Mi Box going to sleep and stops it from dropping off wifi. Might work for Sony / Philips TVs
I don't have this issue anymore since the last maintenance update I got on my X800D. Have you gotten it yet? I believe it mentions the wifi in the release notes.
A maintenance update fixed it for my X800D.
This is also a problem with the Philips android TV's. I have an ethernet connection and can't connect to the TV either while in standby.