Having troubles. Some posts altered, some not.

It should impact all your posts automatically. Unless you select Post Title - Hide for your blog post (see screenshot below), and your blog post header will be hidden.

Depending on the blog header styles that you chose, some have the featured image visible, while others hidden.

If you wish to further customize / hide the featured image, just go to Theme Customizer > Divi Ultimate Blog Plugin > Customize Blog Featured Image > Custom Featured Image Settings > Hide Featured Image

 

For those posts that are not adopting the style set in the plugin, it's because of the backend option that you set for individual blog post.

As mentioned previously, try to edit your post in backend & in the sidebar options: You need to select Post Title option to Show. See screenshot below



If you chose the Post Title option to Hide, then our plugin blog post header will be hidden as well.
**Additional info: The default option for Post Title is Show.

Kindly check.

Two more things to note:
1. Noticed you disabled our blog plugin, try to enable it back.
2. The blue blog header is manually created by you using Divi Builder (see screenshot below). And since our plugin has its own blog header injected manually on every blog posts (after you set the Post Title option back to Show), you will need to manually remove the blue blog header section from your posts using Divi Builder.



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As for the duplicated featured image (see screenshot below):

Just go to Theme Customizer > Divi Ultimate Blog Plugin > Customize Blog Featured Image > Custom Featured Image Settings > Hide Featured Image & the featured image below will be hidden.



Let me know if you need any further explanation.