Unfortunately I didn't think to get the game number and server as this is my first bug report but I was playing a game that ended in a tie and it said that I lost and the other player got a win screen.
I captured a screen shot that can be seen here: https://gyazo.com/e9b729d3e34aa6c095ed7439f23c1f8a
Sorry that this probably is not very helpful but maybe you can find the game through seeing a log of my games and the players I played against.
According to Dominion rules, when having the same number of points, the tie-breaker is the number of turns. In your example, you were the first player and ended the game on your turn with 42 points each. Therefore, you lose. If your opponent had ended the game with 42 points each, it would have been a tie game (same number of turns).