Blinking Monster During "What's Your Poison" Quest

Time: 7:16pm PST
Frequency: Constant
World name: Masamune
Character name: Lyriq Songz
NPC name: Amelot
Monster name: Rockskin Peiste
Class/Level: 28 Arcanist
Party or solo: Solo
In-game time: approx. 7:00pm Eorzea Time
Area and coordinates: Southern Thanalan (17, 11)
Steps:
Step 1. I walked to coordinates (17,11) in Southern Thanalan
Step 2. I attempted to engage monster for quest "What's Your Poison", but he's blinking in and out of frame and won't stay selected/can't be attacked.
Step 3. There was a second Rockskin Peiste roaming that I was able to defeat for quest requirement, but the blinking one stayed present.


System Information:

OS Name Microsoft Windows 7 Home Premium
Version 6.1.7601 Service Pack 1 Build 7601
Other OS Description Not Available
OS Manufacturer Microsoft Corporation
System Name . . . . .
System Manufacturer MSI
System Model MS-7636
System Type x64-based PC
Processor Intel(R) Core(TM) i5 CPU 760 @ 2.80GHz, 2801 Mhz, 4 Core(s), 4 Logical Processor(s)
BIOS Version/Date American Megatrends Inc. V1.8, 7/5/2010
SMBIOS Version 2.6
Windows Directory C:\Windows
System Directory C:\Windows\system32
Boot Device \Device\HarddiskVolume1
Locale United States
Hardware Abstraction Layer Version = "6.1.7601.17514"
User Name Brandon
Time Zone Pacific Daylight Time
Installed Physical Memory (RAM) 4.00 GB
Total Physical Memory 3.96 GB
Available Physical Memory 857 MB
Total Virtual Memory 7.92 GB
Available Virtual Memory 2.89 GB
Page File Space 3.96 GB
Page File C:\pagefile.sys

And on second observation, there are actually multiple "Rockskin Peiste" that are "blinking"/unable to be attacked, present.