Cannot transfer captured carrier to Kushan ally

3v3 game

I captured a Kushan carrier with Hiigaran marine frigate. Considering its just ine big refinery for a Hiig I tried to transfer it several times to a Kushan ally who had 2 carriers on the map. the carrier would not transfer.

I then tried to transfer it to my other Kushan ally who had one carrier on the map and the carrier would not transfer again.

Prior to this I have transferred one refinery to each with no problems and one of them has transferred support frigates without a problem either.

Why can’t the carrier be transferred?