Flickr is always opened after unlocking the screen on Note 4 running Lollipop
I had the same issue, my unlock setup was with the fingerprint reader and the lock screen had live wallpaper of the current weather. At the bottom of that is the "flickr" ad which links to the corresponding photo on Flickr. If you touch that with your finger somehow before swiping your print, it will open when you unlock your phone.

Two choices I found: Stop using the fingerprint reader or change the live wallpaper on the lock screen.