Deleted files still taking up space after emptying trash

I'm on a MacBook Pro running Mojave. I recently copied a folder over 300gb from my main drive to an external drive. I then deleted those files from the main drive and emptied the trash. This was yesterday but the files are still taking space in the hard drive. I looked at daisy disk and it indeed showed over 300gb in "hidden files" but it can't be deleted because the files aren't there. I've never used time machine. I've tried running in safe mode, doing first aid on the drive, resetting spotlight and a bunch other tips I've seen on here but to no avail. It's showing the same amount of disk space on everything. One thing potentially worth noting is that in the "Manage Storage" window it shows I have 900gb of "system storage." I figure that may be tied to the issue, not sure though. Can anyone offer any assistance ? Thanks.