I think this might actually be a Chrome bug, since the problem with the loading images only occurs when there is no featured image added to the posts. Other browsers such as Edge do not show the spinner.
I’ve tested this with Chrome on Mac OS X and Windows 10. The problem still persists.
So what I did was add featured images to each of the posts on the site. The spinner does not appear.
I am closing the topic since the problem is now resolved. Hopefully this will help to further development. Thanks again for your help and support.