Apple Mail
I have random emails go missing and some not arrive at all. (I know this cause fortunately they are arriving on my laptop...and the missing ones are there also). Left hand mailbox menu changes without warning as well. I had a 'All sent' which I use regularly...it is gone.
I have googled; checked to make sure I haven't accidentally deleted; checked I haven't blocked; checked mail settings, POP etc.
Looking forward to knowing if this a shared problem and how I might overcome it. (thank goodness for my old MacBook Pro lap top keeping my mail going...)
Mac is iMac 21.5", latest Big Sur
Laptop is MacBook Pro 13" Mojave 10
iMac 21.5″, macOS 10.14