I created an rstudio cloud project that can be used to run shiny apps (e.g. for teaching). While it worked fairly well initially, now the shiny app greys out when shown in an external browser. There is no error message in the R console, but the Javascript console shows an error like:
shinyapp.js:83 WebSocket connection to 'wss://skranz.rstudio.cloud/11f0ed75a84e47a0b87ab0abd399fa92/p/3620/websocket/' failed:
Error during WebSocket handshake: Unexpected response code: 500
The error arises both under Chrome and Firefox. Initially the error did not arise with R 3.4.4, only under R 3.5. But now I get consistently that problem.
Here is an example project to replicate the problem:
https://rstudio.cloud/project/45034
To start my (RTutor) shiny app, one can simply type:
library(RTutor)
show.ps("Intro", user.name="TestUser")
The project also contains a very simple shiny app called SimpleTestApp that was created by File -> New File -> Shiny Web App. When I open the cloud project and start running SimpleTestApp in an external browser tab, it initially works. Yet, if I then run the RTutor app and afterwards try again running SimpleTestApp, then SimpleTestApp also greys out, with the WebSocket handshake error in the javascript console.
On my local R installation, I never encountered this problem. The RTutor app and my other shiny apps work fine, without Websocket errors.