@magge I know. I was checking everyday 😄

I have figured it out: it's the Engineer Alt Selection mod. It happens when you are trying to SHIFT-order and one of the selected units dies.

irreal missiles are everywhere

You can also interrupt pathfinding with engis on attack move (or SACU/ACU on patrol iirc) and they will lock on to and reclaim a single target using fac attack move range, which can be useful for this scenario.

@Kilatamoro And here you are wrong again...

I just recreated it with Czar. I may be dumb. It happens when 1 hotkey is responsible for several units, and it locks your clicks for you to order with left click. I just had to right click to get out.