@Simon: In fact, this bug seems to be partially fixed: As described, internet connection does not work after activating screen sharing, although the tablet is always connected to my wifi network.
Workaround: After screen sharing is activated, in fact, I can establish an internet connection when I try to connect to another secured wifi network but enter a wrong password. Of course, the tablet cannot connect to that other network, but the tablet remains connected with my wifi network. Then, suddenly, internet is starting to work.
I have no idea, why the workaround works, but it does.
@Simon: In fact, this bug seems to be partially fixed: As described, internet connection does not work after activating screen sharing, although the tablet is always connected to my wifi network.
Workaround: After screen sharing is activated, in fact, I can establish an internet connection when I try to connect to another secured wifi network but enter a wrong password. Of course, the tablet cannot connect to that other network, but the tablet remains connected with my wifi network. Then, suddenly, internet is starting to work.
I have no idea, why the workaround works, but it does.