Blogdown not displaying plots

I have my blogdown site that has been running for a while. When writing a post today I cannot get plots to render when running serve_site().

The plot generates fine when running the .Rmd in interactive mode, it's only when being built by knitting/serve_site/build_site that it doesn't work. The image below shows what I see on the webpage - just that small icon in the bottom.

I know these questions have come up a lot, so just to list the things I've tried:

1. There is no .gitignore under the static directory
2. I've set [markup.goldmark.renderer]unsafe = true in the config.toml
3. I've checked that the figures are being generated (I can see the files under index_files/figure-html)

You can see my blog source here

And the (not working) webpage here