Thanks Metropolitan and all others who are contributing! This thread has been very helpful!
When a mod is pulled from workshop, steam automatically removes it from the game.An old version of "Steeper Slopes" mod which is no longer in workshop (but subscribers will still have it installed) is breaking tunnels - blocking PgDown or something like that.
Not yet known if there's a newer version available (not checked) and if so whether it's fixed.
I just updated the mod. Would be great if you could confirm that the bug is fixed.![]()