The solidify/cut function in assembly belongs to the CAD and this should not have difference in the FEM environment. So what you get in CAD should be the same in FEM.
However this is not always true as I showed in the figure “b” and “c” where cutting half of the model is ok in CAD but is displaced (and meshed) wrongly in Simulate. So I believe that there is a bug here but it can be much related to how the part is model because I could get away of this problem just by modifying the original part (ex. not using project or offset a reference) – don´t ask me way.
I think you are not far away analyzing the way as Creo cuts an assembly. If you analyze the pattern after a cut in assembly you can see extra cut volumes. If In a pattern the volume is not there it means that it was not created. Why it was not created is the open point. It can indeed be that sometimes the plane can intercept “everything” but in other cases it finds an “empty” and the part is ignored.
One could think that choosing the “right plane” like selecting a plane from a part that is also patterned in the same way could overcome this problem. Unfortunately this is not the case because the result is the same.
Even if this is not a “bug” I feel that the command could be more robust with some options to force the cut. I could not find the document again but it seems that you could even set in Creo that to not include some parts when cutting an assembly. So if you can define the parts not to be cut you could also define how all the parts are cut – like a “cut up to”.
Anyway, I got enough examples in this discussion to create the right assembly and not I´m aware now that cuts in an assembly with pattern can have unexpected results.
So if you have the option, avoid it!
Taking the chance, I would like to thank you all for the contributions.