Do you have reproducer for this? It's kinda hard to tell what's going on or mis-behaving from just this information.
sorry for late reply. I can reproduce this issue. One way of reproducing is by changing the salience of the rules and compile it again.
We have upgraded the drools version to 6.x and in that we do not face this issue. Also I tried with version 5.6.0 and it worked fine.