I don't know how long this has been going on, but I suspect since the recent skill updates to this.

I am recently trying a new build and wanted to morph Grim Focus to Relentless Focus. (Have been using Merciless Resolve for quite some time).

In short, RF is dropping once your target dies, if you are fighting a group of three NPC's for example that all agro'd at the same time, it will drop once the last mob is dead. When I mean drop, it doesn't fire, it just goes away.

To be clear this only happens in Cyrodil and not PVE zones.

Merciless resolve does not go away until you either die or fire it, regardless of PVE or Cyrodil.