I have look into this and here is my investigation on your issue. (BTW thanks a lot for sharing the source, it is crucial in this case to have !)
What is odd and should trigger a warning is: I don't see any "wrong loaded" images in your post result: https://erikaduan.github.io/posts/2020-12-31-cleaning-free-text-and-wrangling-strings/#look-arounds
When an image can't load, you should have a broken image link like this usually

If I look at the HTML code with a browser inspector, I don't find any <img> tag here. So it seems that there is nothing written to the HTML as if the results of the chunk were not included.
So I think the culprit in your case is that you used this as global chunk option
This means, every chunk result will be hidden !! Included the result of
```{r, echo = FALSE, fig.align = 'center', out.width = '60%'}
knitr::include_graphics("../../images/2020-12-31_look-arounds.jpg")
```
I think that is why you don't see any image embedded. Try changing this option globally (to avoid further error) or set the default back for this chunk.
```{r, echo = FALSE, fig.align = 'center', out.width = '60%', results = 'markup'}
knitr::include_graphics("../../images/2020-12-31_look-arounds.jpg")
```
Hope it helps.