Preview on save does't work RStudio, but Preview works fine

Question

On RStudio 2022.02.0 open new R notebook, change nothing, check 'Preview on Save', save document, and I get the following console output:

source("~/Desktop/file.Rmd")
Error in source("~/Desktop/file.Rmd") : 
  ~/Desktop/file.Rmd:6:6: unexpected symbol
5: 
6: This is
        ^

The error started on a doc I was working on, but is now occurring on all r notebooks I run. Just pushing the 'Preview' button works fine. I have made no recent changes to the r or Rstudio set-up. The feature worked fine up until a week ago.