I had similar problems for a couple of days, until I realized what the reason is: I had set automatic battery profile switching ON, with the built-in "intelligent" profile to switch to. Turns out that nothing about this profile is intelligent. It actually switches Wifi and Bluetooth off as soon as the "automatic" kicks in, which in my case was between 30s and 1min. The solution is easy: Never use the profile "intelligent". Rather, make a new one "My profile", in which you set everything to your liking. Let the automatic switch to this profile, or switch off the automatic altogether.
After this simple change, I never had problems again.