It depend on the context/group.
At work, no biggie, it just tells me that you acknowledge my message and currently have nothing useful to add.
With my friends, who usually heavily rely on emojis and “oldtimey smileys” (like xD or y.y)? Ya, unless you completely eminate happiness and friendship, I’m concerned about your mood / standing with me.
“Break a leg” (or “Hals und Beinbruch” in German, which is “Neck and leg fracture”).
I don’t even know what the logic could be. Is it supposed to be some sort of reverse psychology?