definitely a light leak -- the fact that they're in the same place in each frame tells me that they're being projected from somewhere in the camera -- on a couple of frames they even look sort of like a stack of books ...
only three possibilities, warped back (unlikely, really obvious), light reflection, or the bellows is leaking. If it crosses the frame line, it's coming from behind, ie, the back. If it's cut off from the frame, it's coming from the front, and that means either a reflection or the bellows most likely.
Reflection? What most folks call light leaks in a Holga is actually this -- look around inside for anything shiny -- can be black or white or chrome or anything. Shouldn't be there, but ya never know. If you find it, paint it flat black with car paint.
ur saying, "bellows?" but those cameras have a cloth bellows around the lens you can see if you focus it back and forth with the back open. If it's got a hole, well, there you are, off to harry fleenor it goes.