I have many Epics with Label "Client-Features", and there are some user stories under these Epics. I want to search all of these user stories, how to write the filter JQL to search them?
You can type
"Epic Link" = "Client-Features"
in the advanced JQL box; if you press the Enter key, Jira will convert the name of the epic to the issue key (e.g. KEY-12345), but it will work as expected.
EDIT: I re-read your question, and I don't think this will work for you. I missed your point of having several epics with a shared label.
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