First thing to note is that WD hasnt updated this app since 2014. Seems as if they gave up on it. Second they say it could take time for pictures to appear in the app due to transferring. I have been waiting 3 weeks and still nothing. Initially all of my pics appeared, but recently (Aug 16) pictures are not appearing. Its better just to use the WD2GO app.
rsalsgiver about WD Photos, v2.4.5