It seems you are using the eazyBI standard calculation to return the average - Create reports.
The calculation would consider the value of zero if it would be present. In your report, the value doesn’t exist, which is why the calculation ignores it. You can see that in the standard calculation formula when you click on it and choose “Edit formula”. Please see the picture and an example of the formula below:
The calculation would still not consider the cases it is empty but will display the calculated value for the members.
There is another option to replace empty values with zero, but that would impact the returned result. You can define a new calculated measure and replace an empty value with a different value with the CoalesceEmpty() function - CoalesceEmpty.