Unable to Attack Monsters Sometimes

Platform: Windows 10
ISP: Cox
Type of Internet Connection: CATV
Internet Connection Speed: 50Mbps
Date & Time: Apr. 11, 2016, ~6:20am CDT
Frequency: Once (did not reproduce)
Character Name: Mondegreen
Race: ElvaanM
World: Shiva
Main Job: Monk, Lv.98
Support Job: Dancer
Area and Coordinates: most of Oldton Molvalpolos, and the area right outside its southern entrance in North Gustaberg
Party or Solo: Solo (additionally, when playing with three Trusts active)
NPC Name: None
Monster Name: Lightning Elemental, Ancient Bomb, Young Quadav, Walking Sapling
Steps:

* Targeting an enemy, bringing up the context menu and selecting "Attack", nothing happened.
* First noticed this in Oldton Molvalpolos against a Lightning Elemental. This was the first monster I attempted to engage in this zone, or even since logging in. I proceeded to attempt to attack other creatures in Oldton Molvalpolos, zoned into North Gustaberg and attempted to attack creatures there, zoned back into Oldton Molvalpolos and attempted to attack creatures there again. The issue remained.
* To determine whether the issue was simply with giving the command to auto-attack, or with any sort of monster interaction, I proceeded to use Chi Blast on the Lightning Elemental. It worked fine, damange was dealt, it aggroed on me, but I was still unable to engage.
* Shutting down the game and relaunching it resolved this issue, at least for the time being.

(There's another bug that occurred a little before and a little after this that I feel might be related, but that's just a hunch; I'll be submitting that bug report momentarily.)