Console error when using API

Bug Report

SpigotMC Username

Please provide your SpigotMC username:

Username: MrRockis

Version

Please provide the version by using the /fb about command:

Version: 
[13:56:42 INFO]: =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
[13:56:42 INFO]: Plugin Name: FeatherBoard
[13:56:42 INFO]: Plugin Version: 6.0.6
[13:56:42 INFO]: Framework Version: 2025-01
[13:56:42 INFO]: Author: Maxim Van de Wynckel (Maximvdw)
[13:56:42 INFO]: Site: https://featherboard.org
[13:56:42 INFO]: Registered to: http://www.spigotmc.org/members/29141
[13:56:42 INFO]: =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

Debug Output

Optionally, include the output of the /fb debug command:

Debug Output: http://paste.ubuntu.com//p/FJJhXfkMGr/

Error Stacktrace

If applicable, provide the error stacktrace:

Stacktrace: When I try using API's scoreboardManager.showScoreboard(player, "duel"); 
It gives this error: https://pastebin.com/9A6Tip02

Expected Outcome

Describe what you expected to happen:

Expected Outcome: Show player the duel scoreboard

Description

Provide a detailed description of the issue:

Description: This error doesn't come always and it's kinda random. Sometimes it works just fine, so I don't think the issue is in the scoreboard's placeholders.
Server version 1.21.4 (latest paper build) and latest ProtocolLib build