If the green gate effect isn't showing up for the monster, there are a few potential issues to check:
Effect Definition: Ensure that EFFECT["EF_NPC_GATE_GREEN"] is correctly defined and loaded in the game's Lua scripts. If there are typos or it isn't included properly, the effect won't appear.
Monster Size/Condition: Verify that the monster's size and conditions in the monster_size_effect_EN.lub file are set correctly for the effect to display.
Conflict with Other Effects: Check for any conflicting effects that may override or disable the display of the gate effect.
Game Version Compatibility: Ensure that the effect and parameters are compatible with the 2022 client you are using.
Double-checking these points may help resolve the issue.