9 month old HP Pavilion came with 8.1 and upgraded to Windows 10. I had some wifi issues early on (constant dropping and red x would show on the wifi symbol). Troubleshooting would fix but would be every 20 minutes so I bought a USB wifi adapter and that worked fairly well. I decided since the laptop was still under warranty I might as well see if I could fix it or if not send it in. Changing DNS to the google DNS fixed the dropping issue, as well documented online, however now if the computer goes to sleep, when it wakes back up the Wifi adapter will be completely gone.
I'll open up Networks and only Local Area Network will show. The Realtek Wireless adapter does not show in Device Manager either. Airplane mode toggling does not change anything, it's simply as if the Wifi capabilities didn't exist. What does fix it is if I go into BIOS and take settings back to default. There is an exclamation next to the Network Adapter that disappears after this is done.
Once I figured this out, I set sleep to off and changed the power settings to maximum performance (as well as changed in dev manager to now allow the device to be turned off). Unfortunately, when I opened my computer lid a few hours later, it was gone again and Bios brought it back.
I am letting the computer sit for several hours without the battery to see if for some reason that fixes it.