Data model or Relationship issue for larger data model

Hi Community,

We have big data model, able to figure out things however stuck with one relationship in data model.

Please find the below simplified (extracted) version of data model.  

Where I need to make below table.

However When I add Complaint_number from dim_complaint table below error pops up.

It says there is no relationship, however you can see relation from the datamodel. I also have tried below things.

1. Tried changing relationship types to both ways

2. Tied merging result code to investigation table but the query keeps running for ever (note Complaint number and Investigation table have the relationship and works)

3. looked at different articles but this specific type i could not find.

You help is much appreciated on this. Thank you.