"Network Protocol Error" disconnect when using BossBar API

[NEZNAMY]

Expected Behavior

Since 1.20.2's configuration phase, server switching clears boss bars. This change should be reflected in the bossbar tracker in some way (ideally resending the bossbars on server switch).

Actual Behavior

Bossbar tracker does not reflect on these changes, thinking the client still can see bossbar(s) while it can not. As a result, using any kind of update action results in a null pointer in the client, disconnecting with Network Protocol Error since 1.20.5.

Steps to Reproduce

Run the following code and switch servers using /server command.

    private BossBar bossBar;

    @Subscribe
    public void a(ServerPostConnectEvent e) {
        if (e.getPreviousServer() == null) {
            bossBar = BossBar.bossBar(
                    Component.text("Server: " + e.getPlayer().getCurrentServer().get().getServer().getServerInfo().getName()),
                    1,
                    BossBar.Color.BLUE,
                    BossBar.Overlay.PROGRESS
            );
            bossBar.addViewer(e.getPlayer());
        } else {
            bossBar.name(Component.text("Server: " + e.getPlayer().getCurrentServer().get().getServer().getServerInfo().getName()));
        }
    }

Plugin List

Custom plugin for reproducing this issue.

Velocity Version

> velocity info
[08:32:57 INFO]: Velocity 3.4.0-SNAPSHOT (git-d9f1016b-b481)

Additional Information

There are basically 2 ways to solve this:

• Resend bossbars on server switch
• Remove player from tracked players

I would prefer the first solution. It will also be consistent with <1.20.2. If deciding for this solution, make sure it's resent at the right time, so there isn't a window during which a packet could slip through before bossbar is resent (just a tip).