On your first problem, this has been happening to me too. This may be a bug, but it is more likely an outdated video card.
Problem number two, truthfully, I have no clue what this could be. I don't think it has anything to do with your video card, but I could be wrong. Most likely, this is a bug.
Your third problem could be any number of things. This could be a bug, or it could be a connection error. Because of my computer's annoying slowness, I can be stuck at a gate for a good ten minutes before it let's me through, and occasionally, all of the enemies in an area just dissapear. They will continue to walk forward until they walk through a wall and vanish, and I will not be able to see any other players or NPCs. This may be your problem. Are you having any of the issues that I am?
The tag discoloration is not an outdated video card because it only appears black sometimes and sometimes one tag will be the right color and one will be black. Also my husband, myself, our kids and niece and nephews all play this game all with computers that are not even a year old. They are different brands and the latest models and the error appears on all the computers. Im not sure what the error is but I dont think its video card related. Good guess though.
