I have a situation where Contact, Account, and Opportunity Ownership is not all the same. We would like so if a new Opportunity is created on an Account, the owner of the Opportunity then becomes the owner of all the associated Contacts on the Account, but not the owner on the Account, only Contacts. 

I made a flow that anytime a new Opportunity is created, get all the Contacts that hold the same Account Id, and reassign the ownership to match the ownership of the Opportunity that was just created. I'm using a Loop element to cycle through all associated Contacts. The ownership is still not changing to the Opportunity record owner for all the Contacts. 

Any suggestions? 

I'm using process builder to launch the flow, using a get records for Opportunity and a get record for Contacts. I'm creating a collection variable for all the Contacts, and looping through that.

Everything works and runs fine, just the owner is not actually changing.