Question HDRP Editor vs Runtime postprocess issue.

We're currently using a custom editor tool to take a bunch of screenshots of predetermined objects in our scenes without any manual work but I've noticed an issue regarding hdrp and post-processing.

When we take our screenshots we disable and enable pre-positioned cameras as we go.
The problem is that when we enable a camera in HDRP if we don't interact with the scene / game viewport it doesn't seem to resolve the post-processing properly.
We get a bright flash of white, and if the window isn't in focus that's all we get in the screenshot.

If the window is in focus it's a better result but there are still post-process artifacts (white outlines for example)

If you drag the mouse around the scene or game view the post-processing resolves and applies properly to the camera view.

We've also just noticed that if we take our screenshots with the tool in play mode everything resolves as expected, but ideally we'd like to be able to do this outside of play mode for various reasons.

Can anyone suggest any reason why this is happening or any way around it?
I'm open to suggestions.

Cheers,
Joe.