Player gets removed from team(vanilla command) after death.
Killing another player makes the player loose the current team they are in, without any log in the console. Tested in all worlds, both op/non-op players.
Paper 1.21.8
plugins: EssentialsX, LuckPerms, WorldEdit, WorldGuard, WorldGuardExtraFlags, Vault, WorldBorder, Multiverse-Core, Multiverse-Inventories, Dynmap, PlaceholderAPI, MyCommand, Residence, CMILib, ProtocolLib, TAB, VeinMiner, BlockLocker, HealthBar-Reloaded
Paper 1.21.8
plugins: EssentialsX, LuckPerms, WorldEdit, WorldGuard, WorldGuardExtraFlags, Vault, WorldBorder, Multiverse-Core, Multiverse-Inventories, Dynmap, PlaceholderAPI, MyCommand, Residence, CMILib, ProtocolLib, TAB, VeinMiner, BlockLocker, HealthBar-Reloaded
Solution
figured it out, it was HealthBar-Reloaded somehow removing player from team when hit/killed
