MoveIt! correctly planning but sometimes failing to execute trajectories

Hello, I am on ROS Kinetic and Ubuntu 16.04 LTS. I have been using MoveIt! for 3 months now and recently discovered a problem that is really bothering me. I am testing the MoveIt!'s OMPL planners in an application where a cutting tool (which is the end effector of a manipulator) has to reach a specific point in a branch of a vine tree, all simulated in Gazebo. This tree is added as an collision object to the program, so MoveIt! is aware of it and should not collide with it. The normal behavior of this application is: I request a plan for the manipulator to go to that point, MoveIt! calculates the path and, If a solution is found, it is executed. However, sometimes MoveIt! says that a solution is found (path well calculated) but then the manipulator exhibits strange trajectories and hits the vine, not accomplishing its goal. This is really strange because it happens with all the planners of the OMPL implemented in MoveIt!, happening more often with some planners than others. The one that exhibits the best behaviour of them all is the BFMTkConfigDefault, failing only 4 times out of 20. I am pretty sure that the controllers of the manipulator are well tuned because I can make the manipulator reach any point that is not a collision object. Plus, the manipulator reaches the point that I want a lot of times (which is not a collision object, of course). Can somebody explain me why the manipulator is sometimes hitting a tree even though MoveIt! says that a solution was found to the path problem and the path was well executed? Thanks in advance, José Brito