Brief bug summary: If you wait too long on the world/channel selection page, you won't be able to log in until you exit and relaunch the client.
More details: If you fail to select a world and channel within some unspecified time, then by the time you do select them you will get the "Having trouble logging in?" message, repeatedly. In order to start playing the game, you will have to close the client and relaunch it.
Steps to reproduce:
1. Log in to Nexon Launcher and click Play on the MapleStory page.
2. Select North America region
3. Wait 10 minutes
4. Select a world and channel
5. Observe "Having trouble logging in?" error dialog popping up.
6. Repeat steps 4 and 5 as many times as you'd like, observe that the error dialog always appears.
7. Exit out of the client and relaunch it (by clicking Play on the Nexon launcher)
8. Select region, and then world and channel, within a minute or two. Observe that character selection page appears and login proceeds normally.
Same for Steam I think. Happened to me a bunch of times in the past but was never patient enough to try repeatedly lol. Same story - start MapleStory, go afk for an extended period of time, then get that message whenever I try to select a channel. I was surprised that the region select doesn't crash if you go afk anymore, but what's the point if you can't get past the channel select screen
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