Image Compression still needs more - what else do I do?

Hey There!
I think I have WP Smush Pro configured really well but my Performance Test Score for Image Optimization is still an 8.

I keep smushing and have smushed everything. There are 3 images that return with an error though that they couldn't be smushed. "Error posting to API: 500 Internal Server Error"

I'm not sure what else to do to get this score higher than an 8?
Please help ASAP as we want to start sending reports to this client and this looks awful on the report having such a low score.

Thank you!