GF front end pod creation form not populating relationship field

(Originally had this on the GF/Pods forum, but not much traffic there)
I have a POD (Ornaments) with about 10,000 records.
I have a Table Storage POD (Collection) which represents a member’s ownership of one of the Ornaments.
There is a one way relationship field from Collection to Ornaments.
I created a GF form to allow signed in users to create a Collection record on the front end. That form is accessed from the Single View of an Ornament record.
I’m dynamically populating post_title, post_id and featured_image_id to the form.
The relationship field is a CF (Ornament) on the Collection Pod. When that field is set to Required the form gets hung up and never creates the Collection CPT. When I remove Required, the form creates the CPT but doesn’t populate the relationship field. (Actually occasionally it does populate the field, but most times it doesn’t)
The post_title and the featured_image are coming across correctly to the Collection record.
I have tried matching both the post_title and the post_id to the relationship field but neither populates the field. Manually I can create the relationship in the back end, by pasting the Ornament post title onto the relationship field and it will find a match, which I then select. When I imported 16,000 of these records, (Using WP all Import pro and CIO) I matched the Ornament Post ID to successfully populate the relationship field. The Relationship field in the Collection POD is set to single select, autocomplete. Should I be matching the Ornament Post Title or Post ID? Is the Relationship field setting of autocomplete correct?