FileBegin error over VPN when exceeding certain file size (RStudio/Shiny issue #2134)

Slight cross-post. I added an issue on the Shiny GitHub repository because my error seems to be related to a specific line in the fileupload.R script. See that post for more details. Posting here as well for the benefit of others and (hoping) for enhanced input.

We are seeing an error in one of our Shiny apps that appears to occur only when running over VPN and only when a file exceeds a certain size (in screenshot below, an Excel file with 322 rows uploads successfully while a file with 323 rows does not). The app is rather complex, so extracting a reproducible example may prove challenging. I'm not finding any references to the error itself.

We are hosting ShinyServerPro on an internal network. The app also runs on ShinyServer (open source) on another server and does not seem to cause the error. In addition, there appear to be some users who do not see the issue when using VPN (our users only see the issue when using VPN).


Has anyone else had this issue? Any guidance on how to further troubleshoot it?