Running KDE 4.13.2 and sometimes when I login I get the folder view on my desktop. Sometimes I do not. This last time I was missing it, I added a folder view widget pointing to ~/Desktop... and now when I started KDE the folder view is back, under the folder view widget I added. It seems completely random whether it shows up or not. Refreshing the desktop does not make any difference... if it is gone it is gone for that session at least.

If you encounter this again, and logout and back in again - do your widgets return to normal?

Well I tried logging off the latest time it happened and the ~/Desktop items did indeed show up... not sure if that will be consistent or if I just got lucky (there is always about a 50/50 chance they will show up). I know killing plasma and restarting it didn't do the trick the one time I tried that.

It is not actually any widgets that are the problem - it is the desktop folder view that seems to be either randomly appearing or not when KDE starts. The widget behavior seems to be perfectly consistent - they are always in the state I left them in - no problems there. I have two Mint 17 with KDE installs with items in ~/Desktop and on one they always appear but on the other, like I said, it is about a 50/50 chance whether they will show up.

So other widgets placed on the desktop are unaffected by this issue? Widgets in the panel are treated differently - I suspect you may be seeing a race condition with the activities functionality, but that can't be the case if other widgets on the desktop (including the desktop wallpaper) are not affected by this.

Is there any log or anything that might have some additional details about what is causing this? Or any way to debug this issue? Logging out does not always fix it either.

I'm afraid i'm not aware of any. This issue needs detailed debugging by a developer unfortunately to be certain of the cause unfortunately.