What is an epic issue?
Certain issues are too big to be handled in a single PR. These issues are tagged with label "epic" either by the developer or the tech lead.
How to work with an epic issue?
Divide the original problem into multiple issues. Each sub-issue should mention Ref issue ####. In this way, Github will automatically link a child issue with its epic issue.
Now, work on these child issues and send PR to close these child issues.
Once all the sub-issues are closed, then assign the epic issue to a QA person. An issue tagged with "epic" should never be closed by a PR. It should be closed manually by a QA.