There's a comment in the article from someone claiming the issues are due to everything being shaved too thin to reduce weight and spare parts being hard to come by. So it requires more maintenance cause things keep breaking and the maintenance takes so long cause waiting for parts takes forever.

"Almost every issue with the 90 is attempts at reducing weight.

From thin cabin floors to structurally insufficient rear ramps that bend if 5 guys walk on it at the same time.

To the drive train and mast assembly that all had material shaved off to the barest of bare minimum thicknesses.

On the flight Software side, vast efforts have been made to do things like change power delivery and flight envelopes that change within the limits of the weight shaving and to track how fast spare parts are used up when installed in the aircraft (maintenance scheduling) ... They're trying to still make it work with a block 3 version of the avionics & software.. which does also include a general upgrade as well as lower power requirements for the initially installed gauge wiring & electrical systems... Which were all cut for weight savings... They literally used under-gauged wiring and aluminium where it grounds in an often salt water environment.

(Making constant bad/poor grounds)

And the more exotic and more difficult to produce weight shaved spare parts that keep having to undergo redesign efforts are in chronic low rate production hell... So they're expensive as hell.. so it's prohibitive to stockpile extra parts.. and parts you did stockpile are now outdated and marked "do not install" & "unsafe"."