I debated posting this, as it has already been reported here; see Lili bug allows her to double heal with Q
However, the thread is 4 months old now and the very serious - and easily exploitable - bug, still hasn’t been fixed.
Basically, hugging an allied hero (so your hitboxes touch directly), while healing them with your Q results in them receiving the healing amount twice. That’s really all there is to it. You can easily reproduce this in try mode by either hugging malf or standing directly over the healing dummy, so I won’t be attaching a replay or anything, but you can imagine how broken this could be if you not only have a Li Li that knowingly exploits the bug, but also a team that coordinates to hug her for double healing.