The infuse iOS app has a few limitations when it comes to playing Picture in Picture background.
When you enable background playback, the default behavior when you switch away is to not be visible (audio only). I have to manually select the PiP button on the playback each time before switching to another app. This should be set as an option (background or background PiP).
The PiP video window has no skip features. Netflix or YouTube both have skip buttons. To skip ahead you have to switch the the full app, then skip, then press the PiP button.