Not showing the image of instagram

Hi,
I posted URL on WordPress after install Oembed plus plugin,
but it doesn’t display the image it is replaced with ‘view this post on instagram’.
So i tried ‘the embed code’, then it worked.
and i posted post’s URL and ‘the embed code’ of same post.
then, post’s URL displayed the image as well!
However, it became doesn’t display the image again if i post ONLY post’s URL and delete ‘the embed code’
I would like to ask you how to display the image by posting ONLY URL if you know.

By the way, WordPress v.4.9.13

Thank you.