Unless you have the custom firmware, you are limited to using the on screen display and remote to find what’s on the disk.
I’d suspect you’ve had a recording which hasn’t ended when it should due to the end signal being missed (assuming you use auto start/stop) and which may still be running.
If a recording is on going, you should see a recording icon on screen when you change channel. If you see one when nothing should be recording that’ll be it.
If you only have (what should be) 8 hours of recording, I’d check each one to see how many minutes are listed. I’d guess there is a limit to how many minutes can be listed though so for an excessive recording the figure may not be accurate, but any that show longer than expected could be a problem.