ETOTAL not Constant

I'm carrying out the drop test analysis of a skid landing gear with Abaqus Explicit. The initial boundary conditions are a downward velocity and a force acting downwards on the center of mass. When reviewing the results, plots for energies show ETOTAL is not constant but varies with time. What could be the reason ? Can it be the magnitude of stable time increments ? Comparing to all the energies plotted, the variation in ETOTAL is not much, so is it safe to ignore this variation? Also, the KE is more than the ETOTAL during a specific time interval. Is this possible? If so, what could be the possible reason? I'm attaching images showing: ETOTAL alone, KE and ETOTAL, and comparison with different energy plots, to give an idea of the various trends.

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Abaqus Explicit ​​​​​​​