Very regularly I get a dialog pop up with the following error. Error - KIOEXEC A folder named /home/user/.cache/kioexec/krun/6746_0/ already exists. It mostly seems to be when clicking a web link from one application other than the web browser. But also happens with other stuff like opening dolphin regularly too... The temporary fix is to just delete the .cache folder. But thats a little frustrating to be constantly deleting that folder.
On a clean install of Kubuntu 17.04 I don't have this bug. However, on another machine I had it in 16.10 and the bug is there after upgrade to 17.04 as well.
I get this issue too in Solus OS when I use KDE connect and choose Browse Device: Error - KIOEXEC A folder named /home/user/.cache/kioexec/krun/10889_0/ already exists. If I remove the folder it still happens and creates a new folder.
I forgot to mention that I use MATE 18.0 and not KDE plasma.
Fixed in Frameworks 5.51 with the fix for 397742. *** This bug has been marked as a duplicate of bug 397742 ***
I just fixed that error case in https://commits.kde.org/kio/3c18acc2229bf0824ee296791329ad74b6313ece -- the fix will be in KIO v5.57. It happened when the remote URL had no filename (i.e. ended with a '/', which can happen over http).