Take a look at this:
It's turn 134, and I've set my AI faction to soak up against an AI Yor on Medium.
My AI is expansionist, and has found a world to settle; that colonizer has been on its way for 10 turns or so.
But now that it's arrived... it turns back. It continues this behaviour (approach, stop, select new destination way back in friendly territory) over and over again, until around turn 185, when the Yor Ai finally colonizes that world.
In the mean time, there are a bunch of amazing worlds about 20 hexes away, explored and inside colonizer range. Completely ignored for over 60 turns while the colonizer goes back and forth by that planet:
Eventually the factions go to war, which I guesss is a distraction, but those worlds are only colonized on turn 312. Indeed, they're all colonized on the same turn by a fleet of 4 colonizers my AI faction sent out at once.
Save files from the above game: