If the position is not set, it will be at default (0, 0, 0). This is a problematic value as it's not particularly clear which direction from the listener (also defaults to 0, 0, 0) the mono sound should be (it does, in fact, have no direction since it's at the same location).
Basically, mono sounds that originate from the same position as the listener can cause issues. The solution is to actively and purposefully move it away. Just a tiny amount can be enough; just place it in front of the listener (to get mono in both sides).
If the position is not set, it will be at default (0, 0, 0). This is a problematic value as it's not particularly clear which direction from the listener (also defaults to 0, 0, 0) the mono sound should be (it does, in fact, have no direction since it's at the same location).
Basically, mono sounds that originate from the same position as the listener can cause issues. The solution is to actively and purposefully move it away. Just a tiny amount can be enough; just place it in front of the listener (to get mono in both sides).