Issue type migration for certain project causing 504 gateway error

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I want to edit an issue type scheme for a project in  our data center instance, where the issue  types Operation Task, Story, and Support all get converted to Task. As of now, there's 454 Operation Task issues, 1300 Support issues, and 11000 Story issues for  this project. So when I try mapping any of the three to the Task issue type, I'm always met with a 504 gateway error.

Is there a better way of migrating these issues, or is there a way to set the proxy timeout longer than what it is already (seems to timeout after 30ish seconds)?

[Brant Schroeder]

@Ian Balas 

Sounds like your system is sitting behind a proxy and the connection is timing out on the proxy.  Are you currently using a proxy?  Have you looked into extending the timeout to keep the session alive?

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Yep that's exactly what it is.

I kind of figured. But again, hoping to find a neat workaround. We ended up asking our ops team to extend the timeout on  our proxy just for us admins. But also, some resources we've researched since then led us to consider the Jira Command Line Interface plug-in to migrate the issue types. So hopefully this works.

Either way, thanks for the input!