Whoever loses due to board fill up always seems to go first.
Is that just me?
The solved conclusion for Connect Four is first player win. With perfect play, the first player can force a win, on or before the 41st move by starting in the middle column.
For the edges of the game board, column 1 and 2 on left, and column 7 and 6 on right, the exact move-value score for first player start is loss on the 40th move, and loss on the 42nd move, respectively. In other words, by starting with the four outer columns, the first player allows the second player to force a win.