i can only guess, but ffxiv doesn't handle switching audio sources. doing so in game will crash it. for example, if you switch from desktop speakers to headphones (depending on how it's handled). i currently have headphones that won't crash the game if i turn them on and off, but that's because the driver doesn't change. but in the past, with different headphones, turning off my headphones (maybe it was unplugging them?) caused my computer to revert to speakers and that would crash the game (or plugging the headphones in)