[Risolto] hreflang not working appropriately on custom posts

Background of the issue:
I have custom posts on my website, and I'm trying to ensure that the hreflang tags work correctly. The site I need help with is link nascosto. An example of a custom post where hreflang isn't working correctly is link nascosto. I am following the documentation at https://wpml.org/documentation/support/adding-hreflang-wordpress/.

Symptoms:
The hreflang tags are not working correctly on custom posts.

Questions:
Why are the hreflang tags not working correctly on my custom posts?
How can I fix the hreflang issue on my custom posts using WPML?