The 'claim victory'-button didn't work

There were some technical oddities in this game: lichess.org/BQoiSh29b5qF

After my 17th move with White I had a winning position (time: w~7min, b~13min). My opponent left the game. When I pressed the 'claim victory'-button after 70 seconds, nothing happened. I pressed again and again, but again and again nothing happened. My opponent's clock just kept running. So I waited for the flag. When my opponent's flag fell, still nothing happened. No score. I reloaded lichess and could not believe my eyes. The game had been scored for my opponent because I had run out of time.

Can anyone tell me what happened here? (I'm pretty sure my internet connection was fine.)

Probably you disconnected, Causing you to think the problem was with black but your clock was running all the time.

Also to be honest you do not have the winning position, black is up a bishop and has much stronger diagonals.

Yeah, if that happened, your internet connection was definitely not fine. If this ever happens again, I normally reload my pages. If it says "Reconnecting", you know for sure you lagged out. Otherwise, ask mods.