You don't have an aggregation problem.
You have a data blend problem.
In order to help you we need more info.
Can you post a fake twbx with your info structure?
Here are some tips where they are suggesting converting aggregate to calculated field
Essentially, the view with necessary dimensions and calculated field for AVERAGE will be another way to handle the error.
Share the file with error and I can give it a shot.
Thank you Luciano (and Dhanashree).
I changed the underlying structure of the data table and this allowed me to complete the calculations without using LOD calculations.
As you can see highlighted in yellow (partial DB displayed).
Many thanks for the help and sorry for the delay in reply - I just got busy once that issue was resolved.