The situation is as follows:

My Zerg Overlords will always retreat when fired upon, and ignore their trigger to move to location and unload.
This is a serious issue as my map requires the Zerg AI Player to capture enemy points by air-insertion.

How can I force my Zerg Overlords to move to location and unload or die trying?

I notice this is an issue with all transports under fire and I've never been able to resolve it unless I make the transport invulnerable, and I can't have that here.

Kind regards,
Viper

make the problem a virtue:

Repeat the unload command every few seconds, so the first overlords will move out of attack range and let others take the heat, until they are all ordered to drop again.

I'll have to come up with a work-around, perhaps time a trigger to order all Overlords to drop at a different, central point. This would send all the remaining ones to attack something significant at least, and then repeat the command as you suggest to ensure they do so. I have to work like this as I want multiple drops at different locations occurring at the same time.

Thank you for the response.

Kind regards,
Viper

Afaik when you give overlords to one of P9-12 they won't turn back. To unload you'll have to give them to an active computer player again.
I'm a bit rusted on the specifics, so I'm not sure if you can give move orders to P9-12 units, but they definitely retain the former order when given. So you could do this:

Start a wave:
[create units, order them to enter overlords, etc.]
Order P8 overlord at "start" to move to "drop"
wait(0)
Give all P8 overlord to P9 at "start"

--------------------

Just always run:
Give all P9 overlord at "drop" to P8
Order unload dropship for all P8 overloard at "drop"

if you can do dat editing just try giving yggrasils patrol idle AI and then using them instead of ovies, they dont have the return to base hardcode iirc