I have no experience with continuous miners but they are drilling through a type of conglomerate which is difficult due to the various hardnesses of the rock making up the conglomerate. If there is a rock of considerably greater hardness on one or the other sides of the drift, I can see problems. Something unanticipated anyhow.
I don't know. These TBMs have been operating all over the world in every imaginable type of subterranean environment for a very long time now.
I find it hard to believe that they're just now encountering a type of rock or soil condition that they're unprepared to handle. The technology is pretty darned advanced these days.