I think the problem is that the date is not a valid ISO format, try to convert it to ISO format and try again.
ISO format is like:
So you can easily split your current string date by the empty space, added a "T" in the middle and ".000Z" at the end, example:
let dateArray = date_pub.split(" ");
date_pub = dateArray + "T" + dateArray + ".000Z";
You even can make a pipe to transform your current date value in a ISO date value, and concatenate this pipe with the angular Date pipe