Q:

What is the difference between 'associations hidden between objects' and 'hidden associations between objects'? 

What is the difference between 'associations hidden between objects' and 'hidden associations between objects'? 
Aren't both referring to the associations that are hidden and not the objects themselves? 

A:

Associations hidden between objects:

There are some associations
They are hidden
Their hiding place is between objects

Hidden associations between objects:

There are some objects
These objects have associations with each other
These associations are hidden

Conclusion:

In the first phrase the associations could be any associations; in the second phrase they are "associations between objects". 
In the first phrase the associations hiding place is "between objects"; in the second phrase they could be hiding anywhere

No, they are not the same.