how to restart cfdem calculation from a certain time

Dear all!
Well, may be it is a silly question, but it bother me a lot. I read that "restart" command can do this function and I tried many times using my own case or the affiliated case (ErgunTestMPI). By adjusting the time step, the solver dump the result of the same time step both in OF and liggghts format. Then I edit the liggghts restart file and read the just dumped liggghts file for continuing calculation. At first it works OK, but a few time steps later It crashed (judging by the output, the particle is accelerated too much and the its kinetic energy is unreal). I know that there may be some round-off errors when recalculate the case from the last time step but it is enough to cause this?! I need some illustrations, thank you!