I don't know if anyone else has used ElumTools with multiple users on the same central model yet, but here goes.
We're in the final rush to get our tender documents ready, and we have 2-3 people working on the lighting at the same time. Our central model is on BIM360 (Revit 2019) and we have 3 multi-user licenses for ElumTools. I noticed today that the 40 odd rooms I had results for in the morning were reset.
Does changing material properties in the Material Manager reset all results? This is the only operation I could think of that would have this effect.
By default, ElumTools will invalidate (reset) all calculations when a model is changed since it cannot verify that these results are valid anymore. You can change this behavior though in the ElumTools settings by changing the "Reset Invalid Results" setting to "False". Since the settings in ElumTools are saved on that specific computer, every user using ElumTools needs to change this setting as well to avoid the problem you're having.
Hope that helps!