I was experimenting with my Reaper form Lich & I noticed that when Reaper form ends, if you have Death Seal active then you get kicked out of Death Seal as well.
This happens with & without the Deadlock node (health reduced to 33% on activation), I’ve not taken the Life Tap node so it’s not that.
You can get it to happen if you go into Reaper form, then just before you time out of Reaper cast Death Seal.
