We are using content search webpart along with Search box and refinement webpart. Also we have applied some custom template to this webpart just to make the look and feel better for content search webpart.
Content search webpart is using managed properties to filter the result based on the search box keyword.
two weeks ago these webparts were working perfectly fine, but now these webparts are throwing error as shown in the screenshot.
Surprisingly, a huge number of users aren't facing any issues, however there are many users (around 300+ ) who they are facing this issue.