When different chess engines play against each other, they don’t always have the same outcome. Why not?

Question

This has bugged me for a bit. If chess engines are meant to always play the best moves, then how come two chess engines playing against each other doesn’t always have the same winner?

In: Other

Answer 1

“best move” is not the same as “only move” or “winning move”.

a game of chess is usually not decided in the first 3 moves, so there is a lot of room for different opening strategies to be considered or acted/reacted on

chess engines also have some artifacts left over from either the programmer OR the historical games used as data sets.