Hi,
does anyone know what happens with my renderings? When rendering to disk, my Pyro looks totally off. When rendering my IPR, it's like it should be. When I save an exr from my IPR, it looks right. When rendering to MPlay, it looks off again. Attached two screenshots.

It should be because of Gamma !
Mplay shows the result with Gamma 2.2 by default.

You should use same Gamma in Nuke.

Thanks for your answer Sadjad, but it's not the gamma. A gamma shift couldn't be responsible for that amount of detail loss.

I just figured out what the problem is: It's missing shadow information. The shadow maps for the lights do not work properly. If I ray trace my entire scene, everything looks in IPR as it does in MPlay and in Nuke. It is when I start using shadow maps that the divergence between rendering to disk and IPR occurs. This is because the IPR always uses raytracing - as opposed to rendering to disk, where you can choose e.g. micropolygonal rendering and make use of shadow maps that you can toggle on object level.

So, somehow shadow maps refuse to work for my machine. Not sure why. If I figure that out too, I'll try to give an update. Until then, I'll be tracing rays

There's lots of reasons shadowmaps can fail, which is probably why nobody uses them anymore. Are you certain the light has an appropriate cone angle, and the map size is sufficient? Are you using static paths for the maps or temp files? Most have moved on from shadow maps as the performance gain is rarely worth the hassle, especially since the main benefit is for static volumes with static lights.

Feel free to post a scene, someone might be willing to help debug.