Although the sprint appears when clicking on project, then issues, it does not appear in the greenhopper plugin in the planning board. Without this feature, the sprint cannot be started and work cannot be planned.
When you navigate to the planning board > configure > click on the issue navigator, are the issues associated with the sprint appearing in your result?
Did you create your sprint using the planning board?
I'm not sure where you are referencing when you say the sprint appears on Project >Issues.
Just a hunch, please re-index your JIRA.
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