My main images are not showing up

Hello,

I am having issues with my main images not appearing on some of my older WordPress posts — and I am not technical at all ??

Below are three instances:

https://www.thisdogslife.co/category/wellness/ (< — slider image)

https://www.thisdogslife.co/7-natural-ways-to-stop-bad-dog-breath/ (main/featured image)

https://www.thisdogslife.co/category/wellness/page/5/ (if you scroll down, all the thumbnail images are gone)

Would anyone be able to explain why these images aren’t showing up and how to fix?

Thank you,

Andrea

The page I need help with: [log in to see the link]