In a shiny app is there a reason downloadHandler() can't render a pdf from rmarkdown::render()?

I have a complicated shinny app, that works perfectly, with the exception of a download button intended to render a pdf from rmarkdown to generate a downloadable report.

In a nut shell downloadHandler() doesn't successfully render pdf from rmarkdown::render(), but Rstudio knits the pdf fine from the .Rmd file, and Rstudio can compile the pdf from the .tex file in temp files without issue.

Simplified code:

My shiny app uses a multi file layout, this minimal code reproducers the problem on my machine with much less complexity than my actual shiny app.

Simple Code that Reproduces the Error

ui.R

#
# This is the user-interface definition of a Shiny web application. You can
# run the application by clicking 'Run App' above.
#
# Find out more about building applications with Shiny here:
#
#    http://shiny.rstudio.com/
#

library(shiny)

# Define UI for application that draws a histogram
shinyUI(fluidPage(

    # Application title
    titlePanel("Old Faithful Geyser Data"),

    # Sidebar with a slider input for number of bins
    sidebarLayout(
        sidebarPanel(
            sliderInput("bins",
                        "Number of bins:",
                        min = 1,
                        max = 50,
                        value = 30),
            downloadButton("Markdown", "Generate report")
        ),

        # Show a plot of the generated distribution
        mainPanel(
            plotOutput("distPlot")
        )
    )
))

server.R

#
# This is the server logic of a Shiny web application. You can run the
# application by clicking 'Run App' above.
#
# Find out more about building applications with Shiny here:
#
#    http://shiny.rstudio.com/
#

library(shiny)

# Define server logic required to draw a histogram
shinyServer(function(input, output) {

    output$distPlot <- renderPlot({

        # generate bins based on input$bins from ui.R
        x    <- faithful[, 2]
        bins <- seq(min(x), max(x), length.out = input$bins + 1)

        # draw the histogram with the specified number of bins
        hist(x, breaks = bins, col = 'darkgray', border = 'white')

    })

    #options(tinytex.verbose = TRUE)
    ##---- Markdown ----
    source('06_Save_pdf_report.R', local = TRUE)
    
})

06_Save_pdf_report.R

output$Markdown <- downloadHandler(
    # For PDF output, change this to "report.pdf"
  filename = "report.pdf",
  content = function(file) {
    # Copy the report file to a temporary directory before processing it, in
    # case we don't have write permissions to the current working dir (which
    # can happen when deployed).

    
    tempReport <- file.path(tempdir(), "07_tester.Rmd")
    file.copy("07_tester.Rmd", tempReport, overwrite = TRUE)
    
    # Knit the document, passing in the `params` list, and eval it in a
    # child of the global environment (this isolates the code in the document
    # from the code in this app).
    rmarkdown::render(tempReport, 
                      output_format = "pdf_document",
                      output_file = file
                      )
    }
)

07_tester.Rmd

---
title: "07_tester.Rmd"
author: "CB"
date: "2/10/2021"
output: pdf_document
---

```{r setup, include=FALSE}
options(tinytex.verbose = TRUE)
knitr::opts_chunk$set(echo = FALSE)
```

## R Markdown

This is an R Markdown document. Markdown is a simple formatting syntax for authoring HTML, PDF, and MS Word documents. For more details on using R Markdown see <http://rmarkdown.rstudio.com>.

When you click the **Knit** button a document will be generated that includes both content as well as the output of any embedded R code chunks within the document. You can embed an R code chunk like this:

```{r cars}
summary(cars)
```

## Including Plots

You can also testingwithout plots, for example:

```{r pressure, echo=FALSE}
summary(cars)
```

Note that the `echo = FALSE` parameter was added to the code chunk to prevent printing of the R code that generated the plot.

Ok the issue and error

If I knit the 07_tester.Rmd file I get a pdf no problem. When I run the shiny app and click the Generate report button, I see normal rmarkdown activity in the console, at the end a window pops up for where to save a file, of note it does not contain the filename in the 06_Save_pdf_report.R code. After you click save button the following error appears in the console:

Warning: Error in : LaTeX failed to compile C:\Users\USER\AppData\Local\Temp\RtmpQD0jkj\file49b85d6276e8.tex. See https://yihui.org/tinytex/r/#debugging for debugging tips.
  [No stack trace available]

No warnings or errors before that, and the app continues to run without issue after. No file was actually saved or downloaded anywhere.

If I go to the C:\Users\USER\AppData\Local\Temp\RtmpQD0jkj\ and open the file49b85d6276e8.tex file in Rstudio, I can compile it as pdf with no error. From the shiny apps attempts the temp folder also contains a texput.log file and it shows:

This is pdfTeX, Version 3.14159265-2.6-1.40.21 (TeX Live 2020/W32TeX) (preloaded format=pdflatex 2021.2.10)  10 FEB 2021 18:04
entering extended mode
 restricted \write18 enabled.
 %&-line parsing enabled.
**C:/Users/USER/AppData/Local/Temp/RtmpQD0jkj/file49b85d6276e8.tex
! Emergency stop.
<to be read again> 
                   \protect 
<*> C:/Users/USER
                  /AppData/Local/Temp/RtmpQD0jkj/file49b85d6276e8.tex 
Here is how much of TeX's memory you used:
 4 strings out of 481250
 115 string characters out of 5913850
 266128 words of memory out of 5000000
 17047 multiletter control sequences out of 15000+600000
 403430 words of font info for 27 fonts, out of 8000000 for 9000
 14 hyphenation exceptions out of 8191
 3i,0n,0p,1b,6s stack positions out of 5000i,500n,10000p,200000b,80000s

!  ==> Fatal error occurred, no output PDF file produced!

I have searched high and low online and not found anything helpful. I must be doing something simple wrong, any pointing in the right direction would be greatly appreciated.