I reported this in-game but decided it wouldn't hurt to do so here. At approximately 0400 CDT this morning I opened a Timeworn Wyvernskin map in the Coerthas Western Highlands. After dispatching 2 Territorial Coblyns ans 1 Territorial Deepeye (all lvl 60) no other MOBs spawned. The progress bar indicated 1 was left to do. Searched area for additional MOBs and found none for the quest. I was unable to open the chest and the hunt timed out after 5 minutes as it was supposed to. Chest was lost.

Character: Rizon Cerberus
Job: Brd
Location: Hyperion, Coerthas Western Highlands, 27,23
Time 7/20/15 @ 0400 CDT
Frequency: 1st time it has happened to me.

Unsure if this is a one time glitch or not. Hope this info helps.