Player remains online in sub-server after BungeeCord disconnect, allowing duplicate login with same UUID

[LPPRR123]

Bungeecord version

BungeeCord-Bootstrap:1.21-R0.3-SNAPSHOT:3cd530f:1974 by md_5

Server version

paper-1.20.4-496

Client version

No response

Bungeecord plugins

AdvancedNMotd-9.1.0
CMIB-1.0.4.1
CommandSync-2.8.3-RELEASE
FriendSystem-Bungee-4.9.8
Plan-5.6-build-2883
TAB v5.2.1
SkinsRestorer
XConomy-Bukkit-2.26.3

The bug

A player can trigger a fake disconnect at the BungeeCord , causing Bungee to consider the player offline, while the player session remains active in the sub-server. The same UUID can then be used to join another sub-server, resulting in two simultaneous logins with the same UUID across different sub-servers in the same BungeeCord network.

Log output (links)

No response

Checking

• I am using BungeeCord and not a fork. Issues with forks should not be reported here.
• I think this is not an issue with a bungeecord plugin.
• I have not read these checkboxes and therefore I just ticked them all.
• This is not a question or plugin creation help request.

[Janmm14]

Without technical details on how a player would be able to trigger this or what accidental race condition or whatever in bungeecord allows this, this issue is quite useless.