title: Fixing a multiple warning "unknown column"
body: <p>I have a persistent multiple warning of "unknown column" for all types of commands (e.g., str(x) to installing updates on packages), and not sure how to debug this or fix it. </p>
  
  <p>The warning "unknown column" is clearly related to a variable in a tbl_df that I renamed, but the warning comes up in all kinds of commands seemingly unrelated to the tbl_df (e.g., installing updates on a package, str(x) where x is simply a character vector). </p>