Dear Todd Hallock,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
As per your description, it seems that error prompts when uploading to SharePoint folder, need to determine the files that have not been uploaded.
If the understanding above is right, as per the test on our side, error for the files that failed to upload can be checked by clicking on the "Progress" tab as shown below after upload:
For your reference: Importing data into SharePoint | Microsoft Learn
Meanwhile, considering that the Progress tab does not last for long, it will disappear after a page refresh, we'd sincerely recommend you upload file using OneDrive sync client to get a more stable connection.
For your reference: Sync SharePoint files and folders - Microsoft Support
What do the OneDrive icons mean? - Microsoft Support
We hope the above can help. If the understanding above is not consistent with yours, please feel free to post back and point that.
Your understanding and patience will be highly appreciated. We hope that you are keeping safe and well!
Sincerely,
Rhoda | Microsoft Community Moderator