I did run into the same issue and forgot to take a screenshot, so I am sharing someone else's reddit post on the same issue. The picture is taken from there:
https://www.reddit.com/r/factorio/comme ... _cheating/
Given how the new Terrain Generation and cliffs were teased in FF-401 to be a great defensive tool I found it odd how biters can simply build a nest that spans both sides. Even the engineer has no access to ladders to traverse cliffs...
It caused me to entirely ignore cliffs again for defensive purposes as they are not reliable. Which is quite a shame given the changes made me actually enable cliffs for my 2.0 playthrough so i had high hopes.
I was hoping that this is considered a bug/unintened behaviour and could get fixed
![Smile :)](./images/smilies/icon_e_smile.gif)
Additional Info: i started my currently playthrouh on 2.0.7 when encountering this behavior - running the latest stable release atm.
It happened a few times as well.