As [id://davidrw] notes, this sounds like a browser issue. It's not clear to me what you are using to save cookies - did you roll your own, or are you using a module? You might check out documentation for HTTP::Cookies::Microsoft and HTTP::Cookies::Netscape. Internet Explorer preserves cookies as individual files. Netscape keeps them in a single file (or cookie jar). What works for one may fail for the other.

You might consider downloading and installing all of the popular browsers, and testing your program on each one. Apparently it works for you with your default browser. Try installing IE, Opera, Netscape, and Firefox, at least.

You may need to test for what browser is being used, and call different code depending on what you discover.