Logged out midgame

Granted I am on a mobile data connection and I have some lag (no larger than 200ms with occasional spikes at 400) but it's pretty stable and don't have issues with any connectivity, since I usually do network intensive work on it with no issues.

I don't really mind the connection dropping and me losing because of it, which rarely happens, but it didn't really drop at all... everything was smooth and I was basically preparing to get the checkmate when the page logged me out of Lichess. I was on the home screen all of a sudden and it took me 3 seconds to log back in but I had already lost the game due to disconnection.

This game: lichess.org/aTgRTaAfLlbq

Please someone explain to me why I was logged out when whatever happened (that will probably be blamed on my connection) took place?

I was playing and somehow I disconnected midgame - a game I was winning. The server declared the game lost even though A) I never left the game, B) had 15 minutes left on my clock and C) had a winning position on the board. Somehow this seems unfair.