Please can you provide a reproducible example of your issue ? we don't have enough information to give good answer. We can just guess what happens.
At least, the complete error message can be useful to know what happened. With Rmd it could come from your document's R code, from pandoc conversion to tex or from tex conversion by latex to pdf. Not easy to know without more information.
Some resources to help provide the useful information
(FAQ: What's a reproducible example (`reprex`) and how do I do one?)