Could your player in in the infamous Auto Defect mode? Using this, the player will connect in MTP mode when possible, but MSC when not. The fly in this ointment is that your computer can only see files loaded in one mode at a time.
So, according to the images you posted your player is now in MTP mode showing the 233 files, 27 folders, Size 1.13GB. I’m guessing the remainder of the memory is taken up by files that were loaded in MSC mode. Try unplugging from your computer, switching to MSC and reconnecting. It’s very likely you’ll discover the rest of the ‘missing’ files.
The key to this conundrum is to select either MTP or MSC (whichever fits your usage needs best) manually and never to use the Auto mode. You’ll probably want to format the device, which will clear the memory and re-load everything in one mode.