Hero image (featured image) is displaying thumbnail-size on Windows

In Windows, the featured images on blog posts are displaying at the thumbnail size, making them look pixellated and awful.

For the example link I provided, going into the post and clicking replace media shows me that this image is 1104 by 883 pixels. In Firefox on Mac it is showing as 1,017px…ok that’s not too bad. On Chrome on Mac it displays at 560 px. I don’t like it but it’s acceptable… however on Windows that same featured image displays at 150 px! Stretching this to hero-width looks awful.

Further confusing things, these are not the settings I have in Settings > Media.

So I’m not sure why it would downsize to 150 px.

I do have a Featured Images plugin that automatically puts the first image in the post as the featured. However, even when I manually select the image it is still doing this.

Further confusing things, I found this post that displays at the proper size on all browsers/operating systems. This post has only one embedded image and it’s 404, which is what made me think of the Featured Image plugin.

Currently I’ve turned off the Auto Featured Images plugin and I’m using Regenerate Thumbnails to delete old and regen *all* the images.

Any ideas what else I might try? I’m not averse to a bit of custom code.

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PS this post crashed first time I posted it but I checked my profile and don’t see it so trying again.

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