Hi,
you get a read timeout when connecting to the job server. However the KNIME log file does not state why. Can you try to see if you can reach the Spark job Server UI via a browser from the machine you are running KNIME on. To do so just copy and past the Job Server URL e.g. http://maskedcluster:8585 into a browser.
For more details you will need to check the Spark Job Server log files which are located on the machine the Spark job Server is running on. The log files are located in the path specified in the settings.sh file which is usually LOG_DIR=/var/log/spark-job-server. Within the log directory you will find the general spark-job-server.log file and for each context a folder with a spark-job-server.log file. Have a look at these files to see what the problem might be.
You can also try to shutdown the Job Server, delete all files in the temporary directory under /tmp/spark-job-server, or whichever file system locations you have set in environment.conf and then restart the Job Server.
Bye
Tobias