I've noticed this, too. I agree that it seems to be very difficult for her to do what most of us have to do in our day-to-day lives - talk to people we've never met. For some people, for all kinds of reasons, this may be a challenge and a source of anxiety and I get that. But for an actress, 'activist', public speaker who has a mic addiction and shameless self-publicist, it seems very strange.
What comes over to me from observing her avoidance of talking to the general public and also dignitaries is
- she holds 'ordinary people' (who are not her fawning fans) in near-contempt. She couldn't believe she was expected to actually STAY at that royal garden party, let go of Harry and make conversation with the masses. She had the attitude, not of a royal, but of a celebrity who might just turn up at an event, pose on the red carpet and then slip out the back. She just doesn't get the need to take an interest in others because she finds them boring and of no use to her. She's typically narcissistic in that, unless talking about herself, she just cannot summon the energy and interest.
2)With dignitaries and 'higher status' people, again she just wants to push in front, shake hands, hear some nice compliments and then doesn't know what to do with herself. There was a video of them sitting on a raised dais (very imperialiastically, ahem...but we mustn't say that - THAT was was W and C did...) with their VIP hosts on a foreign tour and Harry dutifully makes conversation with them throughout the event. Meghan just sits there looking straight ahead with a rictus grin and doesn't make conversation or respond much when spoken to. What the hosts thought of her, I don't know! This was while they were still briefly royal, btw.
I've also seen her literally, physically pull Harry away from a line-up of people who they were scheduled to meet. Harry may be dim and lazy, but he knows how to behave in these situations. You can see him being tugged away and making apologetic faces to the people who'd probably waited ages in line.
Not impressive, Meghan.