Hi @cameronajackson ,
Please check if you have provided proper File Path or Url when you load data from an Excel file using PowerQuery. The standard File Path or Url format as below:
https://xxxxxx-my.sharepoint.com/personal/test1_xxxxxx_xxmicrosoft_com/Documents/Directory%20C/Volunteers.xlsx
Note: The test1_xxxxxx_xxmicrosoft_com represents your email address.
In addition, please take a try to clear cache of your browser, and then try it again to check if the issue is solved. Also please check if you have provided proper credential for this conneciton.
If the issue still exists, you could consider take a try to load data from a web page instead of Excel as below:

Then within the URL box, type the File Path or Url of your Excel file, and provide your credentials for this connection:

More details about load data from a Web page using PowerQuery within CDS, please check and see if the following article would help you:
https://docs.microsoft.com/en-us/power-bi/desktop-use-onedrive-business-links
Regards,
Mona