Issue 1: Can you try using these css codes in your custom css file?

div#fd.eb .eb-entry-article .eb-image-viewport img {

  margin-left: inherit !important;

}



div#fd.eb .eb-entry-article .eb-image-viewport {

  border: inherit !important;

}

Issue 2: May I know what composer did you use when creating that blog post? If you used a different composer to create that post, it cannot be changed later on because different editors contains different functionalities that cannot be carried over. This means that everytime you edit a post, the composer loaded will always be the composer used when the post was created.
Issue 3: It seems your template override file on templates/yourTemplate/html/com_easyblog/blogs/latest/default.php has been heavily customized. Do note that we do not provide support on customization requests. If you want to add the date into the blog listing, you can use the php codes below to populate the post date in the default.php file mentioned above.

<?php echo $post->getDisplayDate($this->params->get('post_date_source', 'created'))->format(JText::_('DATE_FORMAT_LC1')); ?>

Issue 4: Do note that in the frontend, you have to be logged in to preview the post. However, even when logged in, the error persist, which I think the issue is related to sh404sef. We will continue to investigate this because when we tested locally with sh404sef installed, there was no issue.
Can I have the permission to purge all of your Sh404sef extension's SEF URL? Because when SH404sef regenerate the SEF URL, I would like to see if the issue is resolved.
Can you also provide us your FTP access to troubleshoot this issue? Thanks.