I debugged this issue little more and found out the ROS-Websockets from the FlytCloud console are returning error that
drone is not reachable
Current simulator setup is behind an enterprise firewall, so I tested the same simulator outside this firewall and surprisingly FlytCloud console was accessible.
This brings me to the conclusion that our firewall is blocking FlytSim from sending data to FlytCloud, which was not happening couple of days back.
Though the 404 responses from FlytCloud without any error descriptions are misleading.
I request you to provide details of domain/port which are used by FlytSim container to communicate with FlytCloud, so I can add exceptions to the firewall and restore the communications.