Your THD for voltage and current at the input of the drive are not too unusual and show about 2-6% THD voltage distortion and honestly are not that surprising - the predominant harmonics are 5th and 7th (again, not a huge suprise) but elevated for a 24 pulse drive - not achieving perfect cancellation of lower order harmonics.
After looking at the trending and spectrum's, I don't think these are the smoking gun but would have to look more closely at the whole system/model. It is likely that the situation you are monitoring is not the level or event/issue that caused damage.
The failure of the filters on the 18 pulse drive are curious. A filter is generally applied at the "lowest expected harmonic" otherwise, you could AMPLIFY the harmonics that are there. So, here is a scenario - the new 24 pulse drive produces a decent amount of 5, 7, 11, 13 and the 18 pulse drive has an 11th or 17th filter - the filters could amplify the lower order harmonics and fail. Just speculation - lots to understand - I don't even know if both are on at the same time or one replaced the other.
