Possible rutheless bug

If you move out of combat a unit with rutheless and he die , the units close to where you were going to suffer the effect of stunning the same

To confirm, what you're saying is that you have a unit who has the ruthless attribute. That unit, while at low health, moves away from an engagement.

When he attempts to move away, the engaged enemy succeeds at his attack of opportunity, killing the ruthless unit. And then, even though the unit was killed, enemy units adjacent to the ruthless unit's destination hex are stunned as if he successfully moved there.

Is that what was happening?

confirmed bug unfortunately, it has been reported already in the past. Basically if your unit has ruthless, fails the disengage and dies, if the movement path you chose is near other units they get stunned as if it came in contact with them.

[Legulysse]

I confirm it's a bug, it's fixed internally and will come with the next patch.
Please try to not abuse it too much