Hi @AugustDev, Welcome to Dgraph community.
Yes, most of our community is active here and you may expect a quicker response here.
This seems like a bug. The updates are failing for deeper nested mutations. Thanks for letting us know this. I have added the tag to the issue and our team will try to pick it up soon.
EDIT: As mentioned below by @AugustDev, it was a programming bug. 