The 'Recently Saved' and 'Searched For' sections periodically disappear from the Dolphin places panel. I haven't noticed any particular pattern for when this occurs. Restarting Dolphin will temporarily fix the issue. I've tried deleting ~/.local/share/dolphin and ~/.local/share/user-places.xbel but the issue persists.
I'm afraid without reliable Steps to Reproduce, this issue is going to be impossible to debug. Please feel free to re-open the issue if you find a way to reproduce it 100%. See https://community.kde.org/Get_Involved/Bug_Reporting#Steps_to_Reproduce