I loaded my old save few turns before the actual invasion and played in a similar way as before so I have re-created the whole situation.
You can find saves as well as screenshots under following link:
Please note the screenshots are from 2 different invasions on the same planet - like 2 forks from 1 game.
If you load the game from uploaded save all you need is to press "idle ship" on bottom right corner of screen and invade the planet next to ship.
Not sure if this is relevant but I start the game through Steam. Bought Base game with crusade and intrigue DLCs on humblebundle - played the initial campaign map then i decided i'll buy retribution and bunch of other DLCs and after that I started playing a new custom game with custom race. Was thinking that my files might be corrupted somehow because of all these DLCs.
I mean the rules were totally different in the campaign map than in maps from other DLCs and custom maps after DLCs install.