So, this is occurring on Android (my devices) as well as iPhones (Home user's devices) and I can have the same problem on the Web App as well, but posting here since I have a video of it on an Android.
Scrolling through my Movies library creates the app to blank out. Refreshing starts at the top. The problem my devices have is in the mid-S's (though it seems to have issues in a number of spots). But searching for a movie in the mid-S's shows the movie file.
On the Web App, if I click on the "S" on the scrubber, it returns nothing. No movies at all. I have to refresh.
Plex Server Version: 0.9.17.2 (though it also did it on the previous version, I updated specifically hoping it would be fixed).
Android App: 4.26.2.654
Video Of Android: https://goo.gl/photos/EmCUaXDQEoMM8g6y7
Photo Of Web App: https://goo.gl/photos/iMYnZEStMSbMCWFRA
This will be the third bug I have found, but the previous two have zero replies from Plex. Hopefully they can get around checking it out! Thanks!