This is a sporadic issue I've been facing, I value the countdown mode to keep on top of my tickets based on the due date. However, every now and then I will find that overdue tickets will shift to the "No Due Date" field instead of "Overdue".

As you can see in the below screenshow, the red "Open" ticket has an expired due date, although it's showing with a ticket that has no due date. It's fairly easy to see when an item is here wrongly due to the colouring, but this can easily lead to confusion or that ticket being temporarily ignored on accident. 

Although I use script and content blockers I do not have these enabled on any zoho domains, and I've cleared my browser cache a couple times in an attempt to remedy this.