If you filter some mails manually, the filters result in mails being moved into folders with expiry rules set up,  the messages are older than the expiry date for the folder, and the expiry processes while the filter is still in the process of moving the messages, you will get some notifications in the detailed progress area reporting "Failed to copy item, it has no message payload. Remote id: xxxxx". 

Reproducible: Sometimes

Steps to Reproduce:
Possibly not easy to reproduce, but here goes:

1. Set up a filter rule that filters messages into a folder
2. Set the expiry on that folder so that some messages matching the filter would be expired if they were in the folder
3. Select the messages, right-click and Apply All filters
4. Open the "detailed progress" area in the bottom right
[expiry for the folder needs to be processing at the same time, not sure how to trigger this but it happens periodically]
Actual Results:  
You may see "Failed to copy item, it has no message payload. Remote id: xxxxx" in the notification in the detailed progress area. No other ill effects observed though.

Expected Results:  
It seems to me that if one part of KMail knows that the expiry is happening then the filter moving ought to be able to handle when the "collision" occurs without reporting any errors (or not try to move the messages anymore?).

This is with folders and messages on an IMAP resource with disconnected mode enabled.