I am playing my first game of Endless Space 2 and I am very confused about how this is supposed to work. 

I got war-decced by the AI and managed to take two systems that are adjacent to my empire with invasion. Fatia and Canis are now mine, but have no vines/roots/whatever and my vineships cannot spread them. If I order them to and end the turn, the next turn they are idle and the timer to attract the vines is reset. 

What is going on here? Is this a bug or is there some limitation I am unaware of?

Look at this Post: https://www.games2gether.com/endless-space-2/forums/114-bug-reports/threads/26014-unfallen-unable-to-entwine-conquered-system?page=1#post-237854

It is being looked into by the devs.