Debug paste link: https://hastebin.com/egagesevuq.java

Description and relevant errors: https://hastebin.com/mefapedupa.md

Plugin list available if needed

Do you have duplicate plugin jars in your plugin folder?

No, I found out that ProtocolSupportLegacySupport's BossBar module was the cause. I just recompiled it by removing bossbar support for < 1.9 versions and now it doesn't print anymore those errors.

alright cool