I built a water pipe through the tiles under the AETN. at some point the water froze and the tile broke. BUT the tile remains visually there, and I cannot build on top of it to fix the foundation, and my dupes fall through it. Some of the other ancient tiles can be walked through too.
As you can see, in the pic below resources have fallen 'behind' the ancient tile.
Steps to Reproduce
Build a water pipe through the tile and let it freeze
This issue has not been confirmed by a developer yet.