Rubbish typing to be honest, you are correct its a passive Hydrogen maser they use.
Two passive hydrogen masers with 10 -15 Allan deviation
And two Rubidium atomic clocks at 10 -12 Allan deviation.
They haven't had any problems with the Rubidium clocks, they haven't a clue what went wrong with the masers and they were all made by the same company. But the drop in Allan deviation when the second maser goes means its accuracy drops massively.