Suddenly Date Format is not working on WEM & Portal pages

Hi,
We are using WEM 8.5.2 with Portal 8.5. In Some pages we are formating the Date through JSTL. But suddenly the format is not working on English Pages (However it is working fine on Arabic Pages). Once we cleared the Delivery Cache then it started working. So, we are doing this every day from past 10days, We tried to change the code (Instead of format tag, we formatted the date in Java Servlet and then displayed it on Page, but still the date not working properly

NOTE: The site was launched 5years before and we are facing this issue from last 1 week.