I've just played a game:
After I've made move #22 opponent requested a takeback, I tried to accept it but nothing happened, I clicked "accept" again, nothing happened, I tried to refresh the webpage 2 times and Lichess gave me "Internal server error".
Then I restarted my browser and when the game's webpage loaded I see the game finished 2 moves back from the position I've got with my time expired.
After I've made move #22 opponent requested a takeback, I tried to accept it but nothing happened, I clicked "accept" again, nothing happened, I tried to refresh the webpage 2 times and Lichess gave me "Internal server error".
Then I restarted my browser and when the game's webpage loaded I see the game finished 2 moves back from the position I've got with my time expired.