unable to syndicate rss feed | CyberSEO Pro | Support Forum

This means that you have set the plugin to skip the post if the post thumbnail cannot be generated for it (note the Post thumbnail is required checkbox in your feed settings), and you have also selected a wrong source for a thumbnail here, or the feed does not contain any images at all.

In this case it is recommended to check your Post thumbnails settings according to the manual. In case if the importing feed does not contain an image source, you should set the Alternative thumbnail source.

Also please make sure to check this article.

The above feed URL is protected from automated access, and any attempt to download its content will result in a remote server error message: HTTP/1.1 403 Forbidden.

Here is the result generated by the W3C Feed Validator: Login to see this link

Please find more information about it here: Login to see this link

I can't say why this particular feed is blocked, but keep in mind that some Russian government-run resources may even block access from foreign IP addresses after the recent political events.