Dock disappearing when using the Show Recents menu item?
This may be only you, which could be an issue with the preference files, etc. 

Show recents (with a Dock that hides) for me shows the transparent dark screen, and whatever icons that should be there for that app, and shows the dock fully available. 

Once clicking on the desktop though, to get out of this mode, my dock hides again as it should. 

I would recommend removing the Dock preferences, which is located at ~/Library/Preferences/com.apple.dock.plist, and then restarting the dock. 

You should open the Terminal (/Applications/Utilities/Terminal.app), and then run:

rm ~/Library/Preferences/com.apple.dock.plist


then run

killall Dock


to restart the dock. You may have to set up your dock icons again, but this may help the dock not showing back up after using 'Show Recents'