Phpsession failure and user-related issues

Phpsession failure and user string problems: the user name stored in the session on some machines at the beginning, the user name is always lost after the page is crossed. I don't know if it is a header redirection problem. then I added a session_id (SID ); lost, but a new problem occurred for a while. after refreshing the page, the session becomes another user's username. it is estimated that after the session expires, link to other users' php session failures and user problems
The user name stored in session on some machines at the beginning is always lost after cross-page
I don't know if it's about header redirection.
Later, a session_id (SID) is added );
Lost, but new problems have emerged.
After a short time, the session on the refresh page is changed to the user name of another user.

It is estimated that after the session time-out expires, it will be connected to another user?

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Some friends know what is going on. how can this problem be solved?

Thank you.

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What do some machines mean? do you have multiple machines?