I did not find anything posted about this issue after multiple searches using terraforming tiles and a couple other key word mixes.
Some tiles have become blocked for terraforming. The tiles in question have been viewed by multiple players in our guild. Adjusting tiles on either side of blocked tile gives no result. They are out of the 2 full unit spread. IE: 26.1 beside a 24.0 that cant be changed. have tried adjusting the surrounding tiles into range and still no change. Have adjusted tile to the opposite extreme no result. Can not add or remove soil from tile. No visible roots or other blocking growth during regular terraforming. Tile not marked in red on observation screen. If you try to tunnel into it from side it is still blocked from multiple directions and from tunneling up down or forward. so far we have 4 such tiles around our claim. Tile is not solid stone. have even tried pouring water on it. Tile will change to fertile but still be blocked.
Any feed back or news would be nice thank you.