Images and Pics on live site show up or don’t show up half the time

I am redoing my friends company website and added a plugin called unique headers to the theme. The theme we are using is Hestia. I added mainly just some photos from unsplash into the headers of each page. I also added some custom css to each page.

Now, when visited the site, sometimes the icons, background photos, and even the company logo in the footer page of the site will not show. And other times, when reloading the page or even the first time you visit, all the icons, images, and everything show up and load just fine. What could be the problem?

I have updated all the plugins and theme I am using. The only plugins I am using:

Akismet Anti-Spam
All in one SEO
Orbit Fox Companion
Otter
Really Simple SSL
Remove Footer Credit
Unique Headers
WP Forms Lite
WP Mail SMTP

I have deactivated all of them, and tested each one to see if the problem continues. I had to add the footer credit, unique, wp forms, orbit, and otter to start because that is how I get my images/icons and the stock footer out of the way. I still get the same issue.

My photos/images show up in the media library fine. The problem lies in the front-end of the live site where they show up sometimes and others don’t. How do I troubleshoot this? Thank you