The title of the post says it all.
I couldn't figure this one out, but then it hit me...
1. The Slime is automatically generated at the start of the turn from Abandoned Carverns
2. Blood of the Dead is triggered, which reduces it to zero Health
3. The turn starts and as part of the that the Healing sub-phase restores 1 point back to the Slime.
I have updated Abandoned Caverns to create the Slime at the beginning of the Resource phase which now fixes this.