Rstudio server (non-pro) gives frequent (but intermittent) warning as part of all calls

Intermittently, when I execute code in rstudio server (non-pro) I get the following included with calls in R notebooks:

Warning message:
In scan(file = file, what = what, sep = sep, quote = quote, dec = dec,  :
  EOF within quoted string

I also see Error creating notebook: non-numeric argument to binary operator. See line 64. when saving. I'm not sure these are related. I've noticed the problems on both Firefox and Chrome, so I don't think it's a browser specific issue.

Is there some file somewhere I might try deleting to make these issues go away?

The first few lines of my sessionInfo are:

R version 3.4.3 (2017-11-30)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: CentOS Linux 7 (Core)

The version of rstudio-server I'm using is 1.1.419.

Can you provide a small, reproducible example that people can use to test? Warnings can get carried over as code executes, so it could be from a previous bit of code.

I'm not sure what to provide. The warning pops up randomly (but incredibly frequently, and in every session) whether I have a code block that contains 1+1 or has a big long pipe. Often rerunning the block makes the warning go away. I'm trying to convince my colleagues to use R+RStudio instead of Excel+PowerPoint and don't want them to see this kind of thing ever.

I saw a stack overflow post describing the second problem, but their solution doesn't seem to be applicable to the server version. At least I wasn't able to find anything related to RStudio in my AppData.