Grid appears one column only

Please, tell me more

I'm also seeing this issue using a custom theme. In the views admin the masonry javascript targets the rows correctly but when viewing on the front end it displays as a single column.

I think its due to the custom theme using stable as its parent whereas the admin theme is using classy as its parent. Masonry appears to expect certain class names to target the javascript.

For example:

So I think the solution for a themer is to add the desired classes to the correct template. I will try this next and report back.

I can confirm this is the issue. To resolve I copied views-view.html.twig from core/themes/classy/templates/views to the templates directory in my custom theme.

Ideally the module wouldn't rely on specific classes provided by classy theme. Maybe a preprocess hook to add specific classes which can then be relied upon might be a solution?

Looks like this is a dupe of #2716399: Not working on themes based on "stable"