Untargetable mobs in Great Gubal Library

Time: 5am EST
Frequency: Often, but not always
World name: Cactuar
Character name: C'thuuko Tohka
Monster name: Page 64, among others
Class/Level: Dragoon level 59
Party or solo: Party
In-game time: N/A
Area and coordinates: Great Gubal Library x16, y10
Steps:
1. Get to final trash group of dungeon
2. Start attacking mobs
3. After one mob has died, some or all others will become impossible to target

Connection Specs
- Type of internet connection/provider: Rogers cable
- Modem maker/model number: N/A

PC Specs
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Laptop Model Name: Asus N56V
Laptop Model Number: N/A

Gamepad Manufacturer: Sony
Gamepad Model Name: Dualshock 3
Gamepad Part Number: N/A