I have encountered an issue with Atlassian Jira Software Cloud plugins on Jenkins, which is used for connecting to Jenkins for Jira (official) apps on Jira Cloud.

Although the necessary network connections have been established and the certs for the Atlassian site have been added, the error still persists when I test connection from Jenkins: 
Unexpected error when testing connection!
 
With the other local machine which has a similar scenario, it has connected successfully.