Oh, lumen is your only light source?
That would definitely cause some problems then, especially on high. Although this is changing somewhat as the lumen team’s optimizations keep winning perf back, high is generally intended for usable outdoor lighting only. High cuts ray counts and leans more on filtering to get good results; clean indoor lighting requires the Epic setting.
Emissive lighting in lumen is powerful, but it should not be your only source of lighting, especially in indoor scenes and especially on high. That could explain some of your weird ghosting, especially if the emissive is rather bright. I would first try bringing the brightness of the emissive down to about 1/10 of what it is now as a test, and putting a rect or spot light in its’ place, and seeing if that helps.
I’m assuming you have a directional light at least?
Also, for some A/B testing: does the default Unreal Mannequins generate the same ghosting? Does animated foliage?
Also, in case you need to scale perf via using software RT: you’ll want to make sure your meshes are modular (every wall its’ own mesh) and at least 10cm thick, otherwise they’re unlikely to work well with software lumen.