I have setup this custom error page: https://www.zwischengas.com/de/infos/error-5xx.html , it is 241kB big, Cloudflare says it is too large. why? It also does not contain too many characters. What’s wrong?
Obviously Cloudflare does not only count the size and number of characters of the returned custom HTML, it also downloads all referenced images from linked CSS files, even if these are not used. I solved the issue by applying a very small CSS just for the custom pages and now it works fine.