Under review日期变化可能是更换审稿人，增加审稿人或者部分审稿意见返回引起的，从楼主说的情况来看，有可能更换了审稿人或者部分审稿意见返回。

帮你问了意得辑国外专家，他们说审稿状态一旦有变化一般都会很及时的显示在系统上的，不过你这个时间的确是太长了，你可以再发邮件给编辑，如果依然没有回复，你可以发邮件给主编（EiC）主编的联系方式一般在官网上可以找到。

意得辑国外专家回复小编原文：
Possibly the change in status date happens whenever there is some activity in the online submission system. However, your paper has been under review for a long time. I think you should keep sending reminders to the editor. If there is no response, you should write to the Editor-in-chief. Usually, you can find the mailbox of EiC on the official website of the Journal，

good luck

加油