This sounds similar to something that’s happened to me. I went into task manager and saw that there were 10+ Nexon Launchers running (duplicates) and so I ended all of them. When I reopened the Launcher and clicked ‘Play’, MapleStory worked as intended. I don’t know if this will apply to you or not but it doesn’t hurt to try it out?
PS: there’s also cases where the flipside happens too, where the Launcher is fine but the MapleStory program isn’t. It happens when the MapleStory program is running but doesn’t actually do anything- in which case it’s the same procedure. End the MapleStory program and then run it again, usually fixes the problem.