In orbit in proximity to another player in another vessel, after staging or undocking parts that causes the center of mass to change, the CoM is not synced properly causing an offset in the respective views of the other player.

To put another way, before any staging, the vessels are perfectly synced in position and attitude and each player's view is the same as the other. After staging, the other player thinks the staged vessel is X closer or father than it actually is, where X is the offset between the old and new center of mass of the ship.

Reference in this video:
https://www.youtube.com/watch?v=sprH74IsksA
0:37-0:45 - notice the docking node and capsule appear around 3m closer for the left player than the right player. 3m is about the distance between the capsule CoM and the previous ship.

At 2:00 the ship and capsule are touching docking nodes for the left player with a 3m distance, but the right player still shows a 6m distance. I believe the right player's game is correct while the left player's game has stale CoM offset.

Likely fixed a long time ago, I think in the 0.1.5.x dev cycle.