First time with bug after hundreds of hours of playing to cycle 100-140 then starting new base ^^;
I can't fix this bugged tile in sandbox mode. After googling I saw a post that this was fixed. Basically "uknown tile" answers to no one.
Linux mint latest version, please let me know if you need any additional info.
I started a new colony and dug upward and encountered a tile that I couldn't interact with.