FYI: TERA PC Login/Server Entry Issues (2020-01-08) [Last Update: 6:33pm PST)
Right now (as of 1:25pm PST on 2020-01-08) there is an issue that is preventing many people from entering the TERA PC servers. You may not be able to select a server from the server selection screen, or your game may stall when trying to enter a server after selecting a character. If you do manage to enter a server, you may experience extreme instability and lag. This is a known issue and is currently under investigation by the EME team.
Thanks for your patience as these issues are resolved.
Update [2:40pm PST]: Many are reporting that they are able to enter servers again now and lag is back to normal for them, though it doesn't yet seem to be perfect yet. If you are showing a character stuck at 100% loading bar, try closing TERA from the icon in the start bar and restarting the game from the launcher to enter again. You may also consider trying loading an alt if you have more than one character to see if that works and then going back to your main.
Update [4:15pm PST]: Some people are starting to experience trouble again; some people are reporting being stuck in dungeons and issues with IMS. EME has been made aware of the issue.
Update [6:10pm PST]
Update [6:24pm PST]