Original Message

Still more questions than answers.  Wildly out of balance blades would have been noticed at startup.  "Side to side vibrations after landing" sounds more like ground resonance or dynamic rollover.  That could come from a variety of factors (maintenance issue, mechanical failure, botched landing...).  Can't tell from info that's been released so far.  Sad news.

A few more details in this article: https://www.military.com/daily-news/2021/09/07/navy-helicopter-rotor-struck-carrier-deck-causing-crash-killed-five.html