Cubemap not 6:1 on render

Funny thing when I hit render, my cubemap ration changes from 6:1 to something far more squished.
1. I enter 6000 px by 1000 px.
2. Hit Render
3. the long pixel dimension changes!

Any ideas? I’ve already tried restarting SketchUp.
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Hello and apologies for the late response!
Are you able to reproduce the issue reliably?

Kind regards,
Peter