Final answer:
The most likely misconfigured device causing the problem is the firewall, which may have changed or misconfigured rules preventing external users from accessing the application.
Step-by-step explanation:
The device that is most likely misconfigured and causing the problem is the firewall. A firewall is a network security device that monitors and controls incoming and outgoing network traffic based on predetermined security rules. It acts as a barrier between the internal network and the external network, allowing or blocking traffic based on the defined rules.
In this case, since the external users were able to access the application remotely before the replacement of the security device, it suggests that the firewall rules might have been changed or misconfigured. The new firewall settings may be blocking the incoming connections from external users, thus preventing them from accessing the application.
To fix the issue, the firewall rules need to be reviewed and adjusted to allow the necessary connections from external users to the application.