In object mode JS is not loaded for a new instance of an existing object

I'll use the List of users class property for exemplifying the problem.

Steps to reproduce:
1. Have a class, e.g. TestClass, that has a List of users property
2. Create a page that has an object of this type
3. Save the page and exit edit mode
4. Edit the page again in object mode
5. Add a new TestClass object
6. Try to add a user in the List of users property

Expected result:
A drop down with users is displayed

Actual result:
No drop down is displayed and you cannot edit the field

If you inspect the field you can see that the selectize.js code is missing for the select input
Workaround: open the already existing object, which will load the JS needed and will make the drop down work

In the uploaded video it can be seen that there are JS loading issues for other fields as well. I used the Movies Application as an example