When in multiple instances, when you grab an item, it looks fine for yourself and others, but as soon as you let go, behavior is erratic.
For the person who let go, movement is smooth and normal.
For everyone else in the instance, however, it is very stuttery and jumpy, while also taking 3x longer to get from point A to point B. This happens with thrown objects that float slowly or when items are dropped with gravity.
When the item is actively held, behavior is normal until released from the grab.
This was true for all players in the instance, regardless of physical distance from one another (including two people in the same household).
This was only tested on PC.