Using F-secure on an android powered Galaxy Tab S. The subscription lapsed for over a year, but it used to work. Now when I switch on the protection, it switches itself off after 30 seconds.
Have you tried to connect to a different network and see if it helps; for example, connecting to a data network if it does not work on a Wi-Fi network?
Please check this article about VPN disconnecting frequently on Samsung devices.
I haven't tried that yet, but will do when I'm at home. The urgency is over - I can connect from Spain through my phone (Galaxy S9) to watch the football and cycling, so I'll leave it for now.