Tonight I was running Ultimate Mines with two different characters, and a couple times after I was KO'd and revived at the Med Center, when I would return to the Mines through the main teleport I would hear a chime sound and exactly half my HP would be gone.
It didn't happen every time I would return, but it happened a couple times for both characters.
Has anyone else encountered this? Or know if this means something? Or is it just a weird bug?