Manually knitting an Rmd file produces different results when the file is located at different places

When writing a blog post, I often manually knit the document to examine the results (figures, latex formula) quickly, and the output used to be a normal html_document which suits my need. However, after a recent update, manually knitting the document under a blogdown directory no longer produces the html_document output. Instead, it produces something like the following where figures and latex formulas aren't shown properly (taking the default content of an Rmd file as an example):

Here's the output of the "R Markdown" console in RStudio:

/usr/lib/rstudio/bin/pandoc/pandoc +RTS -K512m -RTS 1.knit.md 
--to html4 
--from markdown+autolink_bare_uris+tex_math_single_backslash 
--output 1.html~ 
--lua-filter /usr/local/lib/R/site-library/bookdown/rmarkdown/lua/custom-environment.lua 
--lua-filter /usr/local/lib/R/site-library/rmarkdown/rmarkdown/lua/pagebreak.lua 
--lua-filter /usr/local/lib/R/site-library/rmarkdown/rmarkdown/lua/latex-div.lua 
--wrap preserve -M link-citations=true 
--standalone 
--section-divs 
--template /usr/local/lib/R/site-library/blogdown/resources/template-minimal.html 
--no-highlight 
--include-in-header /tmp/RtmphBPBhs/rmarkdown-str73fd791178f2.html 
--mathjax

If I knit the same document outside a blogdown directory, then the resulting output is as expected:

And the output of the "R Markdown" console is:

/usr/lib/rstudio/bin/pandoc/pandoc +RTS -K512m -RTS 1.knit.md 
--to html4 
--from markdown+autolink_bare_uris+tex_math_single_backslash 
--output 1.html 
--lua-filter /usr/local/lib/R/site-library/rmarkdown/rmarkdown/lua/pagebreak.lua 
--lua-filter /usr/local/lib/R/site-library/rmarkdown/rmarkdown/lua/latex-div.lua 
--self-contained 
--variable bs3=TRUE 
--standalone 
--section-divs 
--template /usr/local/lib/R/site-library/rmarkdown/rmd/h/default.html 
--no-highlight 
--variable highlightjs=1 
--variable theme=bootstrap 
--include-in-header /tmp/RtmpXfya1w/rmarkdown-str724a4171c407.html 
--mathjax 
--variable 'mathjax-url:https://mathjax.rstudio.com/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML

What happens when I click the "knit" button in RStudio? How to adjust the behaviour so that when knitting the document in a blogdown directory produces an html_output file?