This issue is a bit difficult to explain in a good way, but it's consistent and should be fairly easy to reproduce in the right scenario.
During the aliens turn, if an alien pod A does something while they're moving that causes an inactive pod B to gain LOS on your soldiers, that pod B will get a free turn after the activation move.
I'll make an example to explain how the bug works:
Crashed ufo
Two alien pods, one patrol pod A and one outsider pod B
XCom is hugging the ufo door, ready to breach.
During the aliens turn, alien pod A is inside the UFO and runs through the door, opening it. This action causes outsider pod B to gain LOS against XCom and is therefore activated.
The outsider perform their "activation move" and the action shifts back to pod A.
Once pod a has finished their turn, outsider pod B can now perform a normal turn (moving twice/shooting etc) before Xcom has their turn again.
This issue is a bit difficult to explain in a good way, but it's consistent and should be fairly easy to reproduce in the right scenario.
During the aliens turn, if an alien pod A does something while they're moving that causes an inactive pod B to gain LOS on your soldiers, that pod B will get a free turn after the activation move.
I'll make an example to explain how the bug works:
During the aliens turn, alien pod A is inside the UFO and runs through the door, opening it. This action causes outsider pod B to gain LOS against XCom and is therefore activated. The outsider perform their "activation move" and the action shifts back to pod A. Once pod a has finished their turn, outsider pod B can now perform a normal turn (moving twice/shooting etc) before Xcom has their turn again.