Change in "under review" date I submitted a research paper to a journal on 30th July 2015 and its status went 'under review' on 19th August 2015. I did not receive any communication from the journal, so I sent a gentle reminder on 11th Dec. 2015. Unfortunately I did not receive any response again. I then waited until 29th Jan 2016 and sent a reminder email again. Fortunately, the editor replied with "Your paper has been partially reviewed and we are waiting for remaining reviewers' response." The editor assured me that they will encourage the reviewer to submit the response.

Now, the status of the paper has changed from "Under review, date 19th Aug. 2015" to "Under review, date 2nd Feb. 2016".

I do not know what should I comprehend from this change in date?
My guess is that the reviewer they were waiting for has withdrawn or been dropped and a different reviewer been assigned.  There are other internal actions that might cause the same sort of visible change as well, but all of them likely signify progress toward receiving your response.