Yeah the library navigation leaves a lot to be desired, even the keyboard arrow buttons don't work, I can navigate 4-5 thumbnails and then it stops responding.   I just hope Yarp will update P3dO Explorer to work with P8 because that's the best solution I've found so far for viewing my Poser libraries and opening content right in Poser without having to navigate to a specific runtime inside Poser.

Try to open a saved file in a text editor and see what paths you have for textures.   Maybe not all Runtimes have been added?    And by saved files do you mean saved in the Poser libraries or .pz3 files?  I just tried a .pz3 and it opened fine.