Plots not appearing in html produced from Index.md

I'm trying to use markdown to create an index.md file to become the homepage of a package website created through pkgdown . When I use html as the output for the .Rmd files, the plots show up as desired, but when I use .md and then pkgdown converts this into the html homepage for the website, this icon appears along with the grob table for the plot
image
Please advise me how I can get the plot to show up as normal

I'll need more information about your index.md. Is it available online?

No, unfortunately it contains functions etc. I'm not at liberty to publish. The section where I call the plot function in the .Rmd file is as follows:

x<-CustomScatterPlot()

where CustomScatterPlot() is just a wrapper of a ggplot with custom inputs. When I use this to produce a html directly the image appears fine, however, the problem arises when using the .Rmd to output a .md file. The above code produces the following chunk in the index.md file

### `CustomScatterPlot()`

<img src="index_files/figure-markdown_strict/unnamed-chunk-2-1.png" style="display: block; margin: auto;" />