If you're in fullbody, using an avatar with arms shorter than your IRL arms, extending your real arms will pull your VR self's upper chest / head / shoulders.
Doesn't matter if you have any sort of 'FBT fixes' applied - it happens to any model where the arms are shorter.
Example:
This "pull" doesn't happen in non-FBT VR and almost universally just looks bad when it occurs in FBT, especially if you're "resting your arms at your sides" because it'll droop you into a weird "hunchback" position.
Even in avatars of mines which are almost actually proportional to me, there is still very slight tug. I COULD go and change the plethora of avatars I have to have just slightly longer arms, but it'd be much easier if the tug just didn't happen!
Zettai Ryouiki posted a picture of what might be the setting for it, assuming VRChat uses the same script.