Shiny app to create/modify R Markdown Only Succeeds On First Load

I've been following this tutorial:

So far I've managed to get it running with the default report.Rmd file, but when working on my own markdown file I get a peculiar issue. I can pass a couple parameters and everything works smoothly but only the first time I open RStudio. All successive times the shiny app fails to produce a pdf:
! LaTeX Error: Unknown float option 'H'.

This error is pretty generic and doesn't make sense since I can seamlessly create a pdf the first time around. Restarting Rstudio works perfectly fine the first time a report is generated, but fails afterwards.

My thought was it had something to do with envir = new.env(parent = globalenv()) in rmarkdown::render() but tweaking that hasn't yielded anything yet.

Any tips welcome. Thanks!