Thumbnail won't show on posts unless I set featured image

hello wanted to know how to change the images of the carousel ?

@kingstore, don’t hijack other people’s posts please.

Already answered your question here

Modifying my original issue…

So, it has nothing to do with the recipe because when I try to post a regular blog entry, with an image but no featured image, it still does not generate a thumbnail.

Weird, works fine here.
Link to your site?
How did you add this image, with add media?

I’ve same problem.
I’ve selected the following option:
“Either set up a Featured Image for each post, or select to use the last image attached to the post”.
Last article I have not added a feature image but an image within the post.
In latest post list no thumbnail image show (Temptation – di Stefano Giudice):
https://www.oltrecomics.com/home/category/lista-fumetti/

PS: Sorry for my bad English

“Either set up a Featured Image for each post, or select to use the last image attached to the post”.

Yes and works fine here. How did you add that image ? With add media?

Yes, I added with media.

Mmm, sorry I don’t understand, I meant, did you add that image in the post with Add Media?
‘Cause I see you use this “su-box” .. a plugin I think (shortcodes ultimate ?)… Does it have its own control to insert an image in that box?

Do you have this option enabled?
Appearance -> Customize -> Content.. -> Post Lists .. -> THUMBNAILS OPTIONS -> If no featured image is set, use the last image attached to this post.

If yes, and it still doesn’t show up, and that plugin has its own control, could be possible that when you add an image with su, this image it’s not set as post attachment.

Yes I’ve option enable.
Yes, I’ve “shortcodes ultimate” but in another site I do not have “shortcodes ultimate” and I have the same problem
Take a look here (Musicoterapia in gravidanza):
https://assistenzadomiciliare.altervista.org/category/curiosita/

The first one doesn’t work, the second works there.. the second one has a featured image set?

Yes, the second one has a featured image set.

I’m sorry,
I’m not able to reproduce it.
I’ve also downloaded your picture.. ??
You’ve also tried to put that image again in that post right?

Yes, I’ve tried that image again in that post.
Moreover, every new post I open has the same problem.

Ah … I forgot to tell you that until version v3.3.1, Ah … I forgot to tell you that until version v3.3.1, that option worked well

Sorry :O
I wanted to say up to version v3.2