Thanks for sharing. I was able to duplicate your complaint with the file; so there does seem to be a bug somewhere in the software that needs to be examined by Visual Paradigm.
However, not understanding your design, the modeling technique is unfamiliar to me. Not being an expert, I don’t recognize the use of the Association End block shown on your IBD. These blocks seem to have the software defect.
A different modeling technique may work-around the defect.
I noticed that you didn’t create the CIU Internal Block Diagrams underneath the CIU Block in the Model Explorer. Additionally, it’s not immediately apparent to me why there are multiple part associations between the FBW block and the CIU block on the FBW CUI Block Diagram. It kind of looks like a mash-up between an BDD and an IBD.