Due Date is populating for some workflow emails and not for others

Hi

We have timecard approval workflow email with timeout setting as 3 days and 6 days which means approver should receive first reminder after 3 days and second reminder after 6 days.

when approver receives the first email as soon as the timecard is submitted, it does not populate due date as submission date +3 for all emails.

it is behaving very inconsistently where some emails do have due date and some don't and hence 1st reminder doesn't trigger.

any pointers or input to troubleshoot?