I agree to this with the popular view of the Royals just turning up at premiere and galas and state dinners.I think a lot of the issues stem from
1 ) she's American, its not the race issue it's the nationality issue. There is a fundamental misunderstanding of what it means to be royal, and what it means to to be a senior royal. Senior royals work hard (or should do). Its also shown in a lot of American and foreign commentary from countries without a royal family. Royal doesn't equal celebrity.
2) Meghan displays more and more individualistic and narcissistic traits
3) Prince Harry is a troubled man who has not dealt with issues. He has been enabled by the RF and his father (likely through guilt) so he has been babied (also he is the youngest). The worldwide public have also enabled him, he was and is seen as a young royal and a bit of a lovable rogue even though he is almost middle aged
The other main issue is there are big cultural differences between the US and the UK. She had no interest in trying to overcome or understand those, I have a feeling she believed anyone who pointed out cultural differences or gave advice was being racist, when really it was a cultural thing (not saying there weren't racist issues because we know there were, but that was not the majority of people she came in contact with).
She wasn't prepared to compromise on anything, if she didn't get what she wanted (ie red carpet at the wedding) she wouldn't settle for what was offered (blue carpet) she went I won't have a carpet, it will make people think they are being mean to me.
A lot of her issues however were due to her narcissistic personality, and her unrealistic expectations of how things would go, also fed by Harry's lack of support to help her into Royal life.
There is a reason Will waited so long to get engaged he made sure that Catherine totally understood everything she was getting into and what would be expected of her. I suspect that Harry's peabrain just wanted to rush to get a wife and didn't understand his own role (and clearly still doesn't), let alone what hers would be.
Quite why W and C would be expected to help her transition to her role still baffles me, that would be her husband and advisors jobs. I know she expected them to be BFFs but that wasn't realistic given that W & C were at that point moving to become full time Royals with 2 kids and 1 on the way, and H was part time.
She marked her card very early on the the shopping trip fiasco which warned W&C who clearly listen to advice given. Unlike the Harkles who always know better than everyone.