@artioni in the comments found the solution.

Just an assumption, can't be the issue be related to filed name, I refer that is starting with is which in Java is considered getter for boolean field while here you have a String?

The first field with the keyword is within it gets confused with the actual keyword. By simply changing the fields to exclude is, then all data is added to the database correctly.

EDIT: Doing a bit of research helped me understand valid keys in JSON:

Do not use the reserved keywords that are generally used in programming languages. They can lead to unexpected behavior.

In which is is a common reserved keyword in many programming languages.