I just figured it out!
Turns out atleast one level, I tested 4, has to have the fully qualified path to the level for PIE and “Load Stream Level (By Name)” to find the levels from the client perspective.
Thus, I claim, the 4.26.2 Levels tab/functionality is broken in some way in that all of the levels are not fully qualified which will cause an issue with PIE.
So, in addition to having to make your own level streamer, I claim you need to use fully qualified paths to your levels such that PIE will work correctly for your clients.