When you get a drop it won't "yell" it as the game thinks you just "yelled" out that you killed the boss, so in the chat box you get the message " you must wait 7 more seconds before yelling again..."
I assume this is caused from lines 313-316 and 369-373 of src/net/dodian/uber/game/model/entity/npc/Npc.java
As it looks like you changed the code and the client seems to have the yell come from the player, but formatted it to display as [system] ?
p.yell("<col=FFFF00>[SYSTEM]<col=000000> <col=292BA3>" + yell + "@cr2@");
An easy fix could be removing the 10 seconds delay in the yell channel but that's up to you just trying to help