Time: Various
Frequency: Always
World name: Midgardsormr
Character name: Randolont Althoreaux
NPC name: Suspicious Coffers
Monster name: N/A
Class/Level: 50DRG
Party or solo: solo
In-game time: Various
Area and coordinates: various
Steps:
1. Accepted quest from Ponnixia
2. Ran to a Suspicious Coffer
3. Clicked it and there was a hiccup as if the game wanted to open the item menu to use the bomb but menu never appeared.
4. Tried several times to click the coffer and get menu and failed
5. Manually opened my Key Item inventory and used the bomb from there.

Unlike every other quest, it isn't possible to click on the target NPC (Suspicious Coffer) to open your Key Item inventory to select the item to use. You're forced to manually open your inventory and navigate to the Key Items tab.