Outlook Mac - messages only show in Legacy

Using Outlook 16.72.1 on a MacBook Pro OS 13.2.1.

I discovered some emails that I've sent and some I've received only show in Legacy Outlook. I switched to the New Outlook on the MacBook about 2 weeks ago. But, then I noticed emails on my Phone that were not showing on the MacBook. When I flip back to Legacy, Poof! there they are. 

Anyone else seeing this?

Thanks!