I'm not sure if this has happened to anyone else, but shortly before the midwinter festival started I had logged out on a toon of mine. I had logged out standing on top of a house in Eveningstar on the Orien server. Once the midwinter festival had started, I have since been unable to log into that toon. It will start to load, get the loading bar full, and then just sit there indefinitely. I've had this sit for over half an hour once and over 5 minutes on several occasions, both on different days, and mixed between log ins on other toons which btw have had no problem logging in and hadn't logged out in Eveningstar right before the midwinter festival started.
During my time of writing this, I decided to do the transport to hall of heroes as that completely slipped my mind that that was available to me as an iconic toon, and lo and behold, it worked as I'm no longer trying to log into Eveningstar. So if anyone else ran into that issue, there's a possible fix.
So as of now, I guess my point behind this is to look into the possible bug with midwinter festival pertaining to the logging out and back in around the transition to it and to hopefully prevent any future headaches for other players.
Edit: Well apparently it wasn't as fixed as I thought. He's some updated info:
1st: By using the ES Hall of Heroes, once I would go to ES from here, I arrived at the same issue.
2nd: By using the Eberron Hall of Heroes, I was able to move about normally and even go to ES from the harbor to ES cavern route.
3rd: Once finally loaded inside ES and able to move around, my game freaked out freezing me into place and flickering my screen black until finally it remained black (though UI still overlaying it). Note that this happened once I came close to the market area of ES. (ie the area around poison the water)
Going to run some more tests to further narrow down bug culprit.
Edit 2: Well after trying to mess around with some things it would appear that there's a sort of "black-hole" around the area i had originally logged out. You can see that objects have basically vanished around the point. (The point being the NE house in the market section) Of course it could also originate from the northern midwinter NPCs, but still need to check more on that.
Also, once I have entered said "black-hole" I get the crazy screen freakout, become unable to move, and apparently am at 2 places at once. One being where I originally was before the freak out, and the 2nd being surprise surprise, right next to a midwinter NPC.
Edit 3: Probably my last update on this. So first to correct some earlier inaccuracies.
1st: It appears I do retain control of my toon, at least to some degree/some instances. For example, I was able to walk into the "black-hole" from the northern side and once the screen went black, back off and it would return to normal. Well aside from my character having an animation as if I had just teleported and also having my map disabled as if I went into a new area.
2nd: There is no connection with the midwinter NPC's as I originally thought. All that happens is any NPC's within a certain distance will display the above head text in roughly the same area, so no 2 locations at once.
3rd: Rather than "black-hole" i suppose "Black-box" would be more accurate as the void area seems to be more of a square than a circle.
As such,
4th: The point of origin would suggest that my memory of where I last logged out may have been slightly off, as there would be nothing else of interest at that point.
As of now, as long as I don't enter that box, I can play normally. Also as mentioned before, I have only had this issue with this toon who had logged off in ES before the midwinter festival started. That will probably be as much as I can done for this so best of luck to anyone else pursuing this issue.