The Mountain Pass mine is running again. There are deals with DoD and General Motors to establish a price floor, so they don't go bankrupt yet again when the price drops.
The current bottleneck in rare earths is separation. There are four steps - mining, beneficiation (mechanically sorting the good stuff from lots of unwanted rock, done at the mine), separation (sorting out the different rare earths chemically, can be done anywhere), and conversion to metals (smelting). The US doesn't have anywhere near enough separation capacity and Mountain Pass has been shipping ore after beneficiation to China for further processing. That's being fixed, but not fast enough.
Market price and availability swing wildly over about a 4:1 range, resulting in repeated gluts, shutdowns, and bankruptcies. Last big rare earth glut was in 2015, and most non-China production shut down.
