Started a new game after getting the Precursor and Mega Event DLCs, Insane map with 30 civs (I like to have elbow room at start). Just under 200 turns in, and I have now had 3 occurrences of the colonizing event not appearing. None of the planets were Precursor planets. I didn't see anything in the patch notes about a limit on those events, so I'm inclined to think this is a bug.
Since I started noticing the events not appearing, it looks like the success/skip rate is about 50/50. All of the successful events have been Precursor events, although not always on Precursor planets.