Hi Fatemeh,
it is difficult to find the reasons of this without the trajectory file. I guess the quality check analyses (RMSd, fluctuation, HBs, etc.) are not giving any strange jumps, is that right? If so, could you please try to share the topology and trajectory files with me somehow? Maybe with an on-line file sharing service like Google drive? (I know they are big)
Looking forward to your reply.
Regards,
-Adam-