I assume you are talking about a custom agent. Does its access group define a major/minor/patch version for your ruleset that is lower than where you saved the new activity? Did you do a private checkout of the activity or forget to check it back in to the ruleset? What version of the product are you using?
Can you try deleting all the "Agent-Schedule" instances corresponding to the specific agent from Dev portal > Records > SysAdmin > Agent Schedule screen, restart server/jvm and see if your agent gets triggered?
Pushpa, Agent schedule instances are created by your system based out of your Agent rules and are tied to each PRPC node via the node id. These can be safely deleted, as the Master agent will re-generated these when it wakes up. I am suspecting its an environment issue as the same agent runs in another environment.