So, this means that you have to switch versions, if you are in 1.7 or earlier start up your launcher, click on the 'Installations' tab, then click '+ new..', change the name to whatever, but click the version dropdown button, click on anything that is above 1.8, or under 1.14.4, you both are to do this. Also, I recommend removing all plugins with the description that mentions 'BungeeCord', if you don't find any, remove them all, then, add them back 1 by 1.