I have been using WP Super Cache with no problem for some time. Today I decided to add images etc to S3 using CDN Sync tool. I think I did everything correctly as far as uploading the static material was concerned, but when I re-enabled WP Super Cache, all style information was missing. There didn't seem to be any call to the stylesheet in the source.
Disabling CDN Sync eliminated the problem.
Any ideas welcome.