JwtValidator is reading the exp and nbf field as a Java int instead of long:

https://github.com/wildfly-security/wildfly-elytron/blob/master/auth/realm/token/src/main/java/org/wildfly/security/auth/realm/token/validator/JwtValidator.java#L139

This means the maximum expiration date is ~January 18, 2038.  Also, with Javascript a NumericDate this would be a 64-bit value.  The JWT spec also leaves open the possibility of a decimal value so that should possibly be accounted for.