"Not in range", even though obviously in range

First experienced this as SCH trying to apply DOTs, later as WAR where it was much more apparent.

Even when definitely in range (example, as WAR right on top of the mob) I frequently receive the message that I am "not in range" and thus can't attack. Has happened for normal BB combo, tomahawk and overpower. Causes horrible issues with keeping aggro because there are times when literally cannot attack at all.

As SCH for example, even though I was in range to be able to heal the tank (no issues with healing spells incidentally, only attacking) it would tell me I was not in range to apply DOTs to mob.

Time: Since July 17th, continuing
Frequency: Not constant, but frequent
World name: Tonberry
Character name: Creamy Goodness
NPC name: N/A
Monster name: various
Class/level: SCH/50, WAR 45
Party or solo: Party and solo
Race: Elezen F
In-game time: Various
Area and coordinates: Anywhere, definitely camp overlook and dzemael darkhold
Steps:

Try to attack any mob. Am sometimes able to, a second later in the exact same position will tell me I'm not in range. Continues intermittently.