I am on version 2.3.4.RELEASE and am seeing the same issue identified here #24127 except for abstract classes.

Here is the abstract class with the @RequestBody annotation:

Here is the extended class without the annotation:

Postman showing the data being sent in but returning nulls in the object:

If I move the @RequestBody annotation to the class that extends this works. Likewise if I make the abstract class an interface and do not provide the @RequestBody annotation it works as well.