Hi Destac,
Thank you for responding!
I use S3 and Cloudfront for my CDN and I believe the gzipping is coming from W3. I take that from this article:
https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/ServingCompressedFiles.html
Which seems to indicate that s3 and cloudfront serve the gzipped files if wordpress makes them available. However, I also see that there have been issues with serving gzipped content from s3.
I am going to disable gzipping in the browser cache section and see if that helps.