Hi Andrew, thanks for the quick response.
We’ve followed the post process steps again, then taken a look at our lighting setup. We do still have our lightmass importance volume, and it would seem none of our lighting settings have changed. We had a fiddle and disabled our directional light (unticked affects world), and mysteriously, lighting is still completely blown out.
If we save the level and quit, then restart and reopen the level, our post process is broken again, but the lighting is working as intended.
This is almost certainly a bug, I think.
We’re in build 4.5.1.