Go to settings go down to lock screen and security. Go down to the 13th one you will see private mode. Hit it type in your old password go to gallery it should be there. Ill take a gander at the nudes now jkjk
This worked for me (after losing private mode after 8 update) ;
You need to add the Private icon to your settings/toggles menu -
Swipe down from top, extend the toggles menu by it dragging down.
Press the 3 dots in the top right corner. Press Button Order.
Scroll to the bottom, swipe to the next page if you have too anf find the Private Mode icon. Drag the icon to the top with your current toggles. Job done. Now use your private folder like old times
For note 4.. i went into settings. Turned private mode off and then waited 10 seconds. Then turned it back on again ( in settings). Voila.. all my pics returned!! well..that worked for me. Hope it works for you.