Custom normalizers are not respected

I'm trying a custom normalizer with the code provided in #2887372: Add "subfield name" to storage settings for Double Field, for better normalization in core REST, JSON API and GraphQL.

While it seems to work for Rest resources (the normalizer is picked up) for jsonapi is not working.

I changed the priority from 10 to 25 and then I get a fatal error from jsonapi.

"Call to a member function getInclude() on array".

I'm not creating this a bug report because I'm not sure if the normalizer provided in #2887372: Add "subfield name" to storage settings for Double Field, for better normalization in core REST, JSON API and GraphQL is the root of the problem.