In this file https://drive.google.com/file/d/1kgcMsaPilk01euxL-5CHYSqUphjM2Sdj/view?usp=sharing you will find the same code with different GoJS version. One that properly works is named by index.html and it uses GoJS 1.7.12. When group element is expanded links in newer version are not drawn.We don’t know exactly with what GoJS version this problem started but we know it works with 1.7.12. I hope this is enough for you to catch the problem and fix it.
OK, I think we’ve found and fixed the problem. However, it’s a long holiday starting now, so we’re not going to be able to do testing and a release until next week.