So here is what happens and trust me it took me a fuck ton of time to figure this out when I originally used it in L2BattleRoyale. This is also unique to Interlude and I don't think in happens in future chronicles which means they fixed it.
If both players spawned near the area where the initial creation of the packet happens then they can both see it fine because I am assuming you are using current location as the ExServerPrimitive initial center point. However, if you spawned away from where the packet is created then you cannot see it.
In order to fix that you have to store the original Location (x, y, z) of the player when they EnterWorld.
When you create an ExServerPrimitive package you need to provide a name, an x, a y and a z. These values NEED to be the X of the spawn location and the Y of the spawn location. The Z can be -65535 to ensure that the icon will be below the ground.
Once you do that this will stop happening.
Here is how I handle it in Autobots:
Create Circle Packet method
Using EnterWorld location to initialize the package
Storing the EnterWorld location