Hi Jeff, at first glance I was kind of confused because I did not see that 3 solid assembly anywhere visible in the model that you had attached.

Is that 3 solid assembly hidden with the name "trem rout" ?

Keep in mind that I'm not familiar with all the various labels and structure of your model so it's hard for me to know what things I'm supposed to hide and show in order to replicate your problem. If you can set things up in the model that you attach so that the pieces you are asking about are all visible and more obvious that would make it a lot easier to help!

One thing that I noticed was that in the stuff labeled "trem rout", there are not only some solids there but also some extra duplicated surfaces at the bottom of them, here I have slid the solids over to show them:



Is it possible that when you're doing the boolean you are selecting those extra surface pieces along with your solids? If so then that may be causing some difficulty.

Hmm, but also now that I fiddle with it a bit more, the boolean union seems to be having some difficulty figuring out this coincident overlapping area here:



Surfaces that overlap exactly on top of each other like that can sometimes be more difficult for the booleans to process, I'll take a closer look at what's going on there.

- Michael