Dear valued Unreal Engine user,
One option would be to take a capture of the scene using Render Doc or another tool specific to the graphics card. r.rhisetgpucaptureoptions 1 is a useful cvar to use for this.
You could then compare the passed in both the scene captured version and the standalone rendered version for differences. It may be that it parts are rendering correctly until it is performing the tone mapping, or that some specific show flags are not enabled.
Once you have narrowed down which bits are not working, you could then work out which settings need to change to match the standard rendering output.
Thank you for your continued support,