You could also try refreshing Aurena projection and metadata caches to see if that has any effect. Please follow the instructions mentioned in the following post:
(I have no experience in adding new control types via coding, apart from using combination control type standard function. My answer below is for a generic custom field created via entity configurations)
Same thing as happened to me in the past where the drop down , in my case a custom enumeration, was not enabled for the field.
Then I removed the field from the form, unpublished the Entity Contribution and published again. When I added it again to the page, it was happily showing me the drop down.