Content security policy seems to negatively impact styling. There are no reported CSP issues but I can confirm that styling is wrong after applying CSP in our environment and the issue is resolved by removing the CSP.
Issues are not of 3rd party content but rather of basic font colors, background colors, and other styles applied directly to our application.
ChrisFowers wrote:
The simple data reports must include styling and import files during file generation.
My bet is that CSP is preventing these from being included on the document generated.