Rift Herald Bug

I've always been able to solo the rift herald as Yorick. Since the rift herald changes though, it is now impossible due to a bug. The last three times I have tried I have been solidly in the pit fighting. I get it down to around 5% health and it regenerates up to 50% health for no reason. If it was a bug with ghouls taking agro I would think it would respawn at any health level, not just 5%. Extremely frustrating, please fix.