I've searched the forum but can't find any threads relating to this.
I've just been doing the "Witch of the Swamp" adventure.
Before visiting the adventure I sent my geologists out to search Marble and Iron.
I was keeping an eye on when they were going to finish but happened to be visiting the adventure when the time ran out.
I went back to see if they had found anything and they had restarted themselves without finding anything.
This has happened 3 times this afternoon so it is pretty consistent!