Whenever I save an attachment, one CPU core is at 100% load, while the save dialog is open.
The same thing happens when saving an existing mail itself to a file.
(it does not matter by which of the many menus the dialog is invoked)
HOWEVER, only the dialogs in this narrow context seem to be affected.
"Open message in new window" -> File -> Save as -> File: **still** affected
"New message" -> File -> Save as -> File: **not** affected
Also, all other Open/Save dialogs I could find are **not** affected.
As it depends a lot on the context in which a dialog is used, it indicates to me that neither the dialog itself is the problem, nor something it tries to load (like a blocking netshare, but I don't have any anyway)
It should be noted that I get **native Plasma file dialogs**
I could imagine there's a problem in the way (parameters) those specific dialogs are opened.