Upload widget on shinyapps.io shows error in progress bar

After starting an upload, I occassionally receive this error message within Shiny apps deployed to shinyapps.io. I believe it might actually be an issue with shinyapps.io rather than the code of the app itself, as I've encountered it in a few separate apps of ours. More details below--can anyone, especially from the shinyapps.io team, help?

If you select the text and copy, the full text is this error related to openresty/lua/nginx, which are related to shinyapps.io deployment and not the R code of the app itself:

<html lang="en">
      <style type="text/css"> body { color: #222; background: #ddd; font-family: sans-serif; margin: 20px; } h1, h2, pre { margin: 20px; } .box { background: white; overflow: hidden; box-shadow: 1px 1px 8px gray; border-radius: 1px; } .footer { text-align: center; font-family: serif; margin: 10px; font-size: 12px; color: #A7A7A7; } </style>
      <div class="box">
         <pre>/opt/openresty/luajit/share/lua/5.1/lapis/application.lua:68: attempt to index local &#039;curr&#039; (a string value)</pre>
         <pre> stack traceback: /opt/openresty/luajit/share/lua/5.1/lapis/application.lua:68: in function &#039;add_params&#039; /opt/openresty/luajit/share/lua/5.1/lapis/application.lua:394: in function &#039;handler&#039; /opt/openresty/luajit/share/lua/5.1/lapis/application.lua:416: in function &lt;/opt/openresty/luajit/share/lua/5.1/lapis/application.lua:412&gt; [C]: in function &#039;xpcall&#039; /opt/openresty/luajit/share/lua/5.1/lapis/application.lua:412: in function &#039;dispatch&#039; /opt/openresty/luajit/share/lua/5.1/lapis/nginx.lua:181: in function &#039;serve&#039; access_by_lua(nginx.conf:145):1: in function &lt;access_by_lua(nginx.conf:145):1&gt;</pre>
      <div class="footer">lapis 1.0.4</div>

For more background:

  • my app logs in shinyapps.io show nothing around when this happens.
  • I am uploading zipped text files. Sometimes they are not even that big, maybe a few megabytes. The issue has also come up when multi-selecting shapefile components for an upload.
  • In terms of what causes this, I think it might related to load bandwidth situations on my end where the connection during the upload is interrupted, but it's hard to reproduce. For instance, when I'm screensharing (i.e. using lots of upload bandwidth) and showing the app I'm more likely to encounter it, or using a VPN that might have a connection issue.
  • To be clear, this is not about the upload happening slowly or other malfunctions within the Shiny app. The problem doesn't crop up on Windows or Mac local machines, and only rarely comes up on Shinyapps.io deployments (though usually at the worst time when I'm demoing the app!)
  • This stack overflow question seems like the same problem, but the core of the problem is unanswered.

Long term, if anyone from the shinyapps.io team is reading this, if it can't be outright solved, i think it'd be great to somehow have a way to send these errors back to the Shiny server backend so that I can do something with the error programmatically.