What I do is to write my FINAL report in an English Rmd file one sentence to a line. Then I copy a line at a time to Google Translate, paste, copy the translated sentence, and finally paste it in the Spanish Rmd file. That way the sentence numbers coincide and it is easy to re-translate small changes. The final translation of course is done by hand. The code is copied directly from the English Rmd to the Spanish Rmd. It has worked fairly efficiently.
However, this time I made fairly large changes in the FINAL report (English Rmd) and tried to incorporate them later into the Spanish Rmd. Somehow, the file was corrupted and hence the problem. (Note the use of the reflexive keeps me from being responsable.)
I started a new Spanish Rmd, everything from scratch, and it worked.
Hope that this helps.