Display problem: photo thumbnails flash in a single column then disappear

I generated one Flickr API plugin short code by using this Flickr API plugin short code generator that is located next to the Add Media button on every WordPress edit page. BTW: this is a nice touch.

When I view the page, I see the Prev and Next buttons, the photo thumbnails appear for 1 sec and they are all lined up in a single column, then they are gone, all that is left are the Prev and Next buttons. If I view the source of that page all the thumbnails are there, so it must be a CSS issue is what I’m thinking?

I tried another WordPress photo gallery plugin, Awesome Flickr Gallery, and I get a similar symptom, all the photos are lined up in a single column. Wondering if it is my Theme? Anyone else have this issue?

I am using the CLEAN HOME version 1.2.1 WordPress theme which I like a lot because Clean Home is a free small very fast WordPress theme. Authored by this company and looks like this: https://midmodesign.com/ but it appears that Clean Home theme doesn’t work with this Flickr API plugin nor the Awesome Flickr Gallery WordPress Plugin

How do you tell if a theme follows WordPress standards before you start using it?

Any other ideas to get this working?

https://www.ads-software.com/extend/plugins/flickr-api/