I'm also having this issue. I downloaded and ran the beta you linked, and it worked immediately after importing the layout. But if I close AIDA64 and re-open, the images are missing again.
All my images are PNGs with transparent backgrounds.
The peculiar thing to me is that it's not very consistent. Only about half of the images are actually disappearing. As I'm typing this up now, almost all the images of my panel are there, except 2. The red CPU overlay image, and the bottom lightsaber image. The red CPU image is completely gone, as if it were deleted. And the bottom lightsaber image is flashing on and off every couple of seconds.
All of the lightsaber images were spliced out of the same source image, and individually exported through Gimp with the same settings. Same goes for the other icon images.
Let me know if there's any other info that'd be helpful to you.
I attached some screenshots of the various states of my panel from working, not working, and working inconsistently. I also added 2 of the images that are causing problems.