Somewhere along the way I ended up with two versions of my tag for R-related posts (#r and #R), and Hugo didn’t handle the lowercase one. A couple of quick sed lines did the trick to convert both to a more friendly version that Hugo handles just fine. I’m saving them here for future reference in case I ever want to bulk-change a Hugo tag again:

• sed -i 's/^ \- r$/ \- rstats/' *.md
• sed -i 's/^ \- R$/ \- rstats/' *.md