Hard to say, without more details Maybe You should go into root console ("t" from backupmenu main menu), and try extracting backup archives manually, via mounting rootfs and optfs, then, using gtar? I wonder if it really extract BOTH archives. One for sure, as otherwise it wouldn't be looping... Still if You see progress and no errors it is.

If extracting process goes OK, it's not thing related to backupmenu, and Your backups are screwed, somehow. Of course, You can also use root console to fix it *after* restoration - vi is powerful tool But, first, You would need to know what is causing it.

Maybe You have framebuffer enabled in KP? Try recording video of rolling text, and see why it shuts down/reboots? If no, you can renable framebuffer via same method - root console, mounting rootfs, and editing appropriate file. You need to modprobe fbcon early in preinit - search forum for detailed instructions.

/Estel