I was fighting Pianus and was killed immediately after a 1/1 which leads me to think Dragon Blood may have caused it because I've heard this was an issue before. Not completely sure.
I've had this happen to me on multiple occasions. Usually with max achilles, after a 1/1 you should have more than just 1 hp... but I've died couple of times after getting hit with 1/1. Could be lag, could be a dragon blood bug ..but i'm not too sure.