featured image posts

Hi,
first of all congratulations – really beutiful theme. Just installed:)

I have a question regards the featured image(.post-thumbnal). When I open a post there isn’t the the featured image visibile even though I put is in every post and in the previous theme there have been visible. I have controlled in functions.php – there is add_thumbnail with sizes etc.

To present the difference:
my blog: https://obserwatore.eu/wloski-lifestyle/andrea-bocelli/
the other one: https://demo.themepacific.com/imagmag/2008/09/05/readability-test-2/

What I should do?
In advance thanks a lot for your help!