Platform: Windows
ISP: -
Type of Internet Connection: Broadband
Internet Connection Speed: -
Date & Time: Sat April 23rd 10:00-11:00pm GMT +10
Frequency: once/permanent
Character Name: Rogue Muse
Race: Miqo'te
World: Gyshal
Class/Skill Rank: MRD r50
Physical Level: 50
Area and Coordinates: Cassiopeia Hollow (10,5)
Party or Solo: Party
NPC Name: -
Monster Name: Unknown Soldier
In-Game Time: 6-7? Its on the screenshots

Steps:
1. Party headed to Cass to farm Unknown Soldier for items. There was another group there so we spread out to camp.
2. The other group left after they killed it one more time so we had the place to ourselves.
3. When it popped we raced over and started to engage it. As usual with our NM runs we began a series of Battle Regiments for Normal and Weapon skills.
4. In the middle of a BR the Mob did its dissapearing trick and then simply did not reaapear on our screens. The yellow dot for its location marker is visible on the mini map but it is just not there.
5. When our tank uses War Drum it would hit the Mob and we would engage it (the dot would turn red). Also using AOE skills would hit it, so we spent a while running around killing nearby puks and cass to build up TP and the let loose a Brandish or Circle Slash which would hit and we could see the damage message in our chat logs (see screenshots)
6. Eventually we called a GM with the in game service and hung around a while doing nothing. When the GM said there was nothing that could be done we just left.
7. A LS member went down to Cassiopeia this morning and went to look at the spot and it is still there, stuck invisible.