If you have compression issues, try these steps.

1. Install the relevant Adobe DNG converter on your computer:
   Adobe DNG Converter for Mac. First, try using Chrome to download the converter. If Chrome doesn't work, use Safari.
   Adobe DNG Converter for Windows
   
   
2. Restart your computer, and try again.
   
   
3. (Lightroom Classic) Create Smart Previews for all the photos you want to upload and try again.

If you still have a problem, contact support.