I've attached a script to reproduce this behavior and the output of the StateReporter. Is there anything that I need to do differently?
#"Step","Time (ps)","Potential Energy (kJ/mole)","Total Energy (kJ/mole)","Temperature (K)","Density (g/mL)","Speed (ns/day)"
500,0.5000000000000003,-100516778.12917194,-100514547.79711843,118.98305105506671,0.9591993474692536,0
1000,1.0000000000000007,-100515425.77060814,-100511819.93468693,192.36299762377715,0.9591993474692536,2.06
1500,1.4999999999999456,-100514835.4803809,-100510368.56665199,238.29950496707687,0.9591993474692536,1.77
2000,1.9999999999998905,-100514522.33117871,-100509525.64425702,266.5616781910217,0.9591993474692536,1.86
2500,2.4999999999998357,-100514196.04165852,-100508978.46768452,278.3454910015101,0.9591993474692536,1.9
3000,2.9999999999997806,-100514152.50934735,-100508801.46777023,285.465678603462,0.9591993474692536,1.93
3500,3.4999999999997256,-100513990.48632172,-100508530.74921964,291.26433319200413,0.9591993474692536,1.95
4000,3.9999999999996705,-100514099.18439446,-100508432.39956689,302.309849959495,0.9591993474692536,1.96
4500,4.4999999999998375,-100513837.67253573,-100508312.70271303,294.74434780102064,0.9591993474692536,1.97
...
995500,995.4999999833715,-100515995.70435952,-100510307.35485645,303.4602754673055,0.9591993474692536,0.304
996000,995.9999999833597,-100515819.44682398,-100510114.86655764,304.32614910742063,0.9591993474692536,0.304
996500,996.4999999833478,-100515949.61809933,-100510331.93236865,299.6905268216136,0.9591993474692536,0.304
997000,996.999999983336,-100516013.21894117,-100510187.2782918,310.80044455015786,0.9591993474692536,0.304
997500,997.4999999833242,-100515947.76273051,-100510117.73721096,311.01836291642246,0.9591993474692536,0.304
998000,997.9999999833124,-100516183.55732429,-100510327.88930751,312.38633077208556,0.9591993474692536,0.304
998500,998.4999999833005,-100515961.05077694,-100510513.25682221,290.6271939333003,0.9591993474692536,0.304
999000,998.9999999832887,-100515947.95052087,-100510372.42897089,297.4411654058028,0.9591993474692536,0.304
999500,999.4999999832769,-100515917.83395359,-100510158.53726706,307.2451434368191,0.9591993474692536,0.303
1000000,999.9999999832651,-100515956.23833577,-100510335.1903263,299.8698966099735,0.9591993474692536,0.303