QGIS - slow 'Relation Reference' widget type (Feature Attributes window delay)

Question

In Project Properties -> Relations I've defined one relationship between two tables. And when I add a feature in the Referenced layer (parent) I want to be table add its related Referring layer (child) feature(s) in the Feature Attributes window which opens immediately after adding a feature. I was able to accomplish that with setting the Widget type of the Referencing field to Relation Reference. But there is one big problem. The Feature Attributes window opens too late (10+ seconds). It makes it slow. I don't know why it takes too long for this window to be shown when I set the type to Relation Reference. It takes too long after hitting 'Ok' in the Feature Attributes window to close the window and add the features too. How can I improve the speed?

EDIT:

Relation:

Widget type:

Feature attributes window: (slow when we want to show the part shown in this image which is usually opened when the Feature Attributes will be opened which causes the window to open slowly)

The slowness has nothing to do with the parent layer. It's the child layer and that specific field type that causes the problem.

Answer 1

Ok i think the issue is that you did not set up the relation in a right way.

Try the following:Project -> Properties -> Relations

Note: I have several child layers of my "Flurstücke" layer

After that, go to the layer properties of your child layer, edit the widget form to your liking (the attributes under Form Layout are the ones that will appear in your pop-up feature form). If you check out your referencing field, you should see that it is automatically set to "Relation Reference" already. Go to the properties of your parent layer and edit the feature form here. You should see here under "Relations" the relations you set up under Project -> Properties-> Relations.

Drag & Drop them from there to the Attribute Form. None of your parent's layer fields should be set to Relation Reference

It should now work as desired.

Answer 2

There seems to be a problem with making changes in the Attributes Form section . To overcome it I had to change the qgs XML file manually. In the picture below, the left side is the file without this delay problem, the right one with the problem.

Just reset the field config:

<field name="counter_box_code" configurationFlags="None">
  <editWidget type="RelationReference">
    <config>
      <Option/>
    </config>
  </editWidget>
</field>

This solved the delay problem.