Serious question - I think it's nothing new that transport sometimes unload units instantly and sometimes it takes ages for them to unload anything, no matter if the terrain is flat or not (I've tested that on some flat maps, the times were still not consistent) or if it had the drop-command for a long time or a second ago.
For the game experience that results in a RNG-like feeling. 1-2 seconds don't matter that much once the game went on for a bit, but for the first few minutes where players expand with transports it's definitely a huge difference if your transport manages to drop 6 engis in time while getting shot down or if it hovers a couple of seconds resulting in death.
I don't really have a "perfect" replay to show even though I'm sure it happened dozen of times, but just to get a sense of what I'm talking about: #17108149. I played fcking bad there, not talking about that, but either my feelings were wrong there or the transport just hovered for quite some time resulting in its death.
To get to the point: Can someone explain to me how it comes to the different times? Is it due to the ingame-ticks or smth else and more importantly, could it be fixed somehow or is it just smth to live with?