I had the same problem with that specific avatar a few months ago. It seems the Skin modifier in 3Ds Max doesn't have the correct skin weights (both the Max model and the exported avatar have this issue).
I guess it was the first time that I used her, so I hadn't encountered the issue before. I wanted to open a ticket, but it was faster for me to simply reskin the model and I forgot about it afterwards
Sorry I couldn't reply earlier.