We had the same problem and figured out the cause. If players are at different zoom levels then the ping will not be accurately placed, but if they are on the same level of zoom it will be accurate.
I.E. If players are at 100% zoom, and a DM is at 50%, each players ping will not appear in the intended spot to the DM, and vice-versa, but all of the players can accurately ping to each other because they are on the same zoom level.
I don't know what the deviation is. As a temporary fix make sure everyone is at the same level of zoom.