This is rather useless, specifically since it is missing the data file. Furthermore, if you want to have somebody have a closer look, it has to be possible to reproduce the effect you are seeing with only a small number of processors and rather quickly. Thus you need to produce a small test system and reduce the number of timesteps between the different stages.
The plot you are providing is rather useless. If you want to observe whether atoms are evaporated, you need to monitor (and thus plot) the number of atoms in the system.
Furthermore, you need to visualize your system and see if there is a significant change happening during the “drop” in kinetic energy. Does it affect the temperature/pressure or potential energy?
You don’t explain which LAMMPS version you are using, what platform you are running on, what your command line is and so on.
Just dumping the input on people and thinking this explains everything is overestimating the capabilities of people answering here and somewhat rude. People are the more likely to help you, if they see that you are making an effort. At the moment this is not the case. Please see the forum guidelines for some more explanations and examples.