Virtual world border size lerping/isInside() is desynced when same border is shown to multiple players

[AnttiMK]

Expected behavior

When multiple players are shown the same virtual world border, WorldBorder#isInside(player.getLocation()) should return true when the specified player is inside the border.

Observed/Actual behavior

Minecraft.2026.01.06.-.01.10.36.11.DVR.mp4

Steps/models to reproduce

1. Create a virtual world border, show it to a player and lerp the size
2. Observe isInside(player.getLocation()) correctly returning true vs. what client is seeing
3. Show the same border to an additional player
4. Observe isInside(player.getLocation()) now returns false even though the player is inside the border according to the client

Plugin and Datapack List

Test plugin: https://pastes.dev/lslLStCk8f

Paper version

[22:44:34 INFO]: This server is running Paper version 1.21.11-69-main@94d0c97 (2025-12-30T20:33:30Z) (Implementing API version 1.21.11-R0.1-SNAPSHOT)
You are running the latest version

Other

No response