HUMS analysis is only as good as the signal picked up by on-board accelerometers.
A shame the data is not recorded - surprising also.
Planetary systems are notoriously difficult to record early symptoms. This is due to the signal loss through the carrier to another bearing before it can get to a nonrotating hard mount. On direct locations adjacent to bearings, they are very good at picking up small benign issues. On planetary systems a defect noise is faint, and washed out by all the other planet clash that passes around the ring.
Absence of HUMS signal does not mean absence of problem in the epicyclic. In fact if there was any sign previously, then it was probably already more developed, enough to actually affect the planet clash by large deflections.