Moving mail messages takes a very long time /hangs

Sometimes when moving mail messages to a local folder things don’t advance beyond the “This Operation may take a while to complete.” message.  If I kill the MailClient process and restart it, it will work ok again for a while.

Hello Scott,
are you perhaps moving large amount of messages or messages with large attachements?
What version of eM Client are you running? Check the full number in Help>About section.

Regards,
Olivia

I had this same issue, it was traced to a couple of emails among the batch I was moving. Any batch containing either of these would put up the Moving it might take some time and hang with only solution being killing EM by task manager and restarting EM. Same for move or copy, on or offline mode.
These two emails were blank with a spinner when clicked on. I deleted them and after that could copy large number of messages without difficulty.