Any reason an invasion battle wouldn't occur?

[Rogue]

Okay, I've done a little searching on the forums and didn't see anything to answer my question so here goes.

Using the stock install of SEV, patched up to 1.25, my friend and I are playing a "hot seat" version of SEV. He tried to invade an enemy home world. The Troop Transport launched the shuttle carrying his invasion troops and they "hit" the planet without being destroyed by an WP's. We had the little inverted triangle over the planet with a Mech inside, signifying ground combat was to occur as well as the corresponding message about it taking place after the turn was over. Combat ended, and nothing happened. No report, no feedback of a battle that was auto-resolved, etc. That was some 10 odd turns ago with no information on what happened to the troops.

Was this a freak occurrence, or is there something else at work here that we missed? I've invaded other planets under version 1.20 with no issues so I'm curious if anyone else has had this show up, or we need to take something else into consideration before invading.

I've not had a chance to try it again to see if there's a different outcome, but I did start a fresh single player game to try and test this without playing it hot seat.

Thanks in advance for your help!