Hello Victoria Herring,
Thank you for using Apple Support Communities and for sharing these details with us. We want you to have a good experience when using your Mac. If certain folder are not displaying the correct details, such as size. We would like to help isolate this issue by recommending some steps you can try.
First, we want to make sure that this issue is isolated to your external hard drive. Try dragging the affected folder to your desktop. Then "get info" to see if the correct size details populate. If the correct details populate for you, this might be an issue with reading the external hard drive correctly. We might have to repair the disk: How to repair a Mac disk with Disk Utility - Apple Support
If the folder displays "0" in size while the folder is on your desktop, then we can try the steps below for more troubleshooting:
1.) Restart your Mac to help refresh things: Shut down or restart your Mac - Apple Support
2.) If you have any pending updates, it would be a good idea to install them. Keeping your Mac fully updated can help resolve various issues: Update macOS on Mac - Apple Support
3.) If you're already fully updated to your most compatible macOS version, then we can test this issue in safe mode. This step can help isolate possible software related issues: How to use safe mode on your Mac - Apple Support
Intel processor
1. Turn on or restart your Mac, then immediately press and hold the Shift key as your Mac starts up.
2. Release the key when you see the login window, then log in to your Mac.
3. You might be asked to log in again. On either the first or second login window, you should see ”Safe Boot” in the upper-right corner of the window.
Depending on your results, follow the steps under “If the issue continues in safe mode” or “If the issue doesn't continue in safe mode”.
We hope these steps help you out. Thank you for using Apple Support Communities. Take care.