Bugged region score calculation?

When I played recently with my mate I noticed a situation that didn’t seem to be as intended:

We went to forest region to kill some rivals.
The region level was at about 14 with an appropriate region score.
After killing just one rival the region score and level dropped immediatly to 0.

That didn’t happen when I recently played in farmlands when I destroyed a reaper. Yes, it dropped a bit, but still was high enough that a few minutes later another reaper spawned in.