File Sizes (including hidden files) don't sum up to total data usage

I recently noticed that my Galaxy S9 was running low on space. While using the 'My Files' app that comes with the phone to do some spring cleaning, I noticed that my Internal Storage shows a usage of about 47GB. However, something doesn't add up. I open that folder, turn on display of hidden files, and select EVERYTHING that is listed. The result is only 13.72GB!?!?!?!?!!! This is WAY WAY off. I have a huge amount of space getting used (over 30GB) and no idea what is actually using it, nor how to clear it out. I have tried using cache cleaners, like Norton Clean, but those only found about 1GB of residual files, etc. I have also tried restarting the phone, but this doesn't help either... Other than a factor default reset, I can't think of anything else to try. Can anyone help me figure out what is going on?