Loosing hero's


I am not sure what is going on but I lost wu long. I had 2 one I was working on was at level 27 I believe. I went to level him up and even though I had him locked he is now not in my arsenal now. Just disappeared. I have been curious about Loosing hero’s seems to happen a bit. But now I know it is happening. Can you see if this is a bug or game problem please? Wasn’t sure until I noticed wu long the one I started leveling up. The one at 1 was still there.