Hi Bastian,
Please also send the full request URLs for these requests:
.../plugins/servlet/scroll-viewport/bootstrap.js?...
.../plugins/servlet/scroll-viewport/control/...
Both of them must contain the query parameters pageId, spaceKey, and viewportId.
If these parameters are missing the requests URLs for the CSS files you mentioned will not get their cache key path segments replaced,
resulting in the URLs you sent.
If these requested CSS files can't be resolved due to the invalid URL I bet you get an HTML error / 404 page instead with a text/html
content type.
Thanks,
Jens