Just tried rebuild folder on my Sent folder in eM Client 8. This was after I had to use another mail client to upload sent items to the correct sent items folder (had to put them somewhere else in eM Client first).
They still wouldn’t show in eM Client sent folder, so I tried a repair folder.
In v 7, this would empty it and then download everything again.
In v 8 it just empties it, and doesn’t try to download again.
Something else broken in 8.