Misty A

HI,
It was not installed recently, however I disabled it. Still no results.
There are also no plugins recently installed (i.e. in the last 6 months)

Hi! yes, it is solved. Sorry for not letting you know earlier. The solution was pretty simple: in the WordPress Related Posts plugin advanced settings>default thumbnails>”used custom field for thumbnail” needed to be ticked and set to “post-image”
thanks for support

Hi Petra, thanks for quick reaction. The only new thing was to enable the Disqus for comments…
My plugins are: Broken Link Checker, Disqus Comment System, EU Cookie Law Compliance, Google Analytics, Google Analytics Dashboard for WP, Jetpack by WordPress.com, MailChimp, Popular Widget, Regenerate Thumbnails, SEO Internal Links, Shareaholic, Simple Follow Me Social Buttons Widget, Top 10,
WordPress Related Posts, WordPress SEO.