I wonder if you are using a date-and-time field instead of a date field.
Since I noticed that depending on the time zone you set up on kintone's user account and the date-and-time field value, the argument that you pass from a date-and-time field after creating a Date object can be changed like in your case. Therefore, I would suggest using a date field if you are using date-and-time field now or try Moment.js to format the value of a date-and-time field instead of creating with a new Date object.
Here is the info about Moment.js.
▼ Moment.js - customize date formats
Regarding the different value in the test and production environment, if I put the same value on a date-and-time field, I got the same result. Here is how I went to the test environment for your reference.
▼ Previewing an App