Possible cave shard closing upon rift closing

I have never had my caves shard just up and close on me before, but for some reason the cave entrances are blocked up indicating that the caves server isn't active. 

It's very odd, I can't fathom why this happened. The only thing I can think of that is of note, is that the rift was nearing its end, and the mimics were still near the entrance. (also they are still replacing the shadow trio which is not great.)