Win and iPhone why do they erase Cookies themselves?

Question

HTTP Cookies

In the authorization form, there is a hidden field where 5 random characters are inserted stored in the cookie, if there is no id_user variable in the cookie in which they are stored, js creates and writes randomly generated characters there for 365 days.
The problem is that for some unknown reason SOME users lose this id_user 1-2 times a week and create a new one. This has been seen by Win and iPhone users. - 100% they don't clean anything with their hands. Why is this happening?

Answer 1

Safari stores cookies set on the client for no longer than 7 days
To store longer, you need to set cookies on the server side
More about safari itp 2.1 here https://webkit.org/blog/8613/intelligent-tracking-...