Duplicate emails keep appearing when syncing to POP3 account

This problem occurred several months ago and is happening again today.  EMclient keeps downloading old emails from server.  I am running POP3 with option to save copy of email on server after download for unlimited time.  I have deleted the duplicates and they have returned on the next sync.  Anything changed lately?

It may be some database corruption. Close eM Client and run C:\Program Files (x86)\eM Client\DbRepair.exe. See if there is any difference.