Hi Daniel,
The model looks fantastic!
I don’t know why that is happening with the red Material, just from looking at the screenshots, but if Separating the handle fixes it, than that’s a perfectly valid way to solve it.
If you want to know what is happening exactly (I suspect it’s a slight error in the model), then you can upload your .blend file to Googledrive, Dropbox, or so and post a link here, so we can have a look and try to troubleshoot.
