This issue may occur if the work period in question has a time off during the period, and if the time off type is not included in the overtime rule.
Since there is a time off in the period, and overtime rule does not have the timeoff type added to it, the overtime rule would omit the hours for the timeoff and calculate the overtime based on the remaining days only. The hours added due to this may not have the hours more than the normal working hours.
Include the required time off type in the overtime rule settings.
Steps to add the time off type to the overtime rule:
Log into the Web TimeSheet as the administrator.
Click on the administration tab in the top menu.
Under Timesheet setup in the side menu, click on Overtime rules.
In the Overtime rules list, double click on the name of the overtime rule to be edited or click on edit button beside the rule.
In the Include Time Off click on the drop down and select the timeoff type(s) that has to be included in the overtime rule.
Click on Save.