Server hosting vivaldi.com/blog is sending invalid HTTP Response headers
As FYI, https://vivaldi.com/blog/feed/ is sending invalid HTTP Response headers.
It always sends these headers (regardless of the content and actual time):
Last-Modified: Fri, 31 Mar 2017 16:17:39 GMT
As a result, feed readers may think that there is nothing new although there is. Please check the server/blog platform configuration?
I pinged the web team to investigate this issue.
Got a workaround from our web developer until the frontend will be fixed.
The header issue was fixed.
For the curious, this was caused by what appears to be a bug in Wordpress, which I reported as https://core.trac.wordpress.org/ticket/47968