The following has been published to the US Test Server on May 31st:
- Revisions related to current live event and LoA-specific content. Please note! Resource changes only; will not be visible to Test Server players.
- Corrected certain melee attack-related latency issues.
- Corrected certain hotkey-related latency issues.
- Corrected an issue with castle tax rates as reflected in NPC merchant pricing.
- Re-enabled the “/lang korean” command (minus quotes) and game option.
- Re-enabled the “/englishonly” command (minus quotes) and game option.
- Corrected a potential crashing issue with dismissing certain summoned monsters.
- Updated appearance for High Pet Collar.
- Dismissed tames and resurrected monsters can no longer be tamed with Tame Monster.
- Advance Spirit effect now also disappears when player is killed.
- Earth Bind can no longer be cast when player is invisible.
- Turn Undead can no longer be cast on dead creatures.
- Spell-effect icons will now be displayed on two lines when enough spells are in use.
- Dice Daggers can no longer deliver “critical” attacks on castle gates.
- Corrected an animation display error for those using ranged weapons without ammunition.
- Corrected various text errors.
Source: NC Testing Forum

Corrected certain melee attac
Corrected certain melee attack-related latency issues.
That's a complete lie, I tried test server and it is just as bad as the normal servers. Nothing changed regarding the swing delay.