Error opening files on RStudio server (running on an Ubuntu VM via Google Cloud Platform)

I'm not entirely sure if I should be directing this question at RStudio, Google, or Ubuntu...

When trying to open a file to run analytics on it using RStudio server, I consistently receive this message:
Error in file(file, "rt") : cannot open the connection

I have checked the file path - I tried both relative and absolute paths, and also changing the working directory within RStudio - and added read and execute permissions to all associated directories.
Any ideas on what the problem could be?

The error message is pretty straight-forward, implying the file-path provided does not lead to an existing file. (I think most people in this forum have seen this error many times!)

With exploritory data-analysis, I usually debug this error by trying to load the file via RStudio's "Import Dataset" GUI in the Environment tab, which in turn creates a snippet of R-code and prints it to the console as the file is loaded.

Are you loading this via via something like shiny or rmarkdown?