Hmm weird, just a sanity check you’re using Windows right? Only windows platform has 4.9 support, Mac is currently only compiled to 4.7, and Linux is unsupported.
This is an interesting problem and it has everything to do with how rigging is currently set up. The character is rigged such that you do not get micro motions from animation while still maintaining relative head offset and causing the body to turn and twist with your body leaning. It is a set of compromises to fit all the tracking criteria and may not be suitable for all applications.
In VR, it is generally a bad idea to add animation motion to your hmd as it will encourage motion sickness, so if you wanted someone to sit you would play the sitting animation and keep the head IK(from camera/animbody) in the rough area where your head is while sitting. Your head mesh is automatically hidden so small mismatches won’t be visible, large mismatches will however have the character bend in unrealistic ways like the one you have where the head height is much lower than normal.
All animbody positions are given relative to the character root with Y-forward orientation, you may need to adjust this if you want a different kind of functionality. You could have the animation centered around the head not moving, or you could change the rigging to accommodate what you want to achieve. I haven’t personally done a sitting character so I don’t have a ready to go solution for this…
Full character rigging in VR is a complex issue with compromises abound; a standard approach is to not have a body for this reason e.g. you can use the Echo hands character and not worry about fully body rigging at all, but I encourage you to explore and share your solutions so we can have one more thing solved in VR 