Expected behavior: Master Yi disappears for 1 second upon casting Alpha Strike, and during that time Alpha Strike scans for targets to mark for damage. Marking the same target more than once deals 25% damage to that target instantly, up to 3 times. After 1 second, Master Yi reappears and all marked targets take damage.
What actually happens: If Master Yi has 2 or more targets available, Alpha Strike behavior is normal. If there is only 1 target however, Master Yi reappears 0.2 seconds after casting Alpha Strike and deals no additional damage. (This was the behavior of Alpha Strike before 9.10.)