"Could not connect to the R Session on RStudio Server" error message is usually used by an error in the connection between RStudio and R Session. There are several possible reasons for this:
R Session crashed or unexpectedly closed: In RStudio, if the R Session crashes or is unexpectedly closed, you cannot connect to the R Session, resulting in a connection error. You can try restarting the R Session, or restart the entire RStudio Server application.
R Session cannot be started: If R Session cannot be started, the R Session cannot be connected and a connection error message is displayed. You can try to check that the R Session is configured correctly and that you have enough system resources to start the R Session.
RStudio Server cannot communicate with R Session: If RStudio Server cannot communicate with R Session, it cannot connect to R Session and a connection error message is displayed. You can try to check that the network connection is up and ensure that the port of R Session is not blocked by a firewall or other network security measures.
R version incompatibility: If the R version is incompatible between RStudio Server and R Session, you may not be able to connect to R Session, resulting in a connection error. You can try to check if version R is compatible and upgrade or downgrade version R.
To solve the above possible causes, try the following methods:
Restart the R Session and RStudio Server applications, or restart the entire server.
Check that the R Session is configured correctly and that you have sufficient system resources to start the R Session.
Check that the network connection is normal and ensure that the port of R Session is not blocked by a firewall or other network security measures.
Check whether the R version is compatible and upgrade or degrade the R version.
