Strange ASP. NET session loss problem, for help!

Strange ASP. NET session loss problem, for help
I encountered a very strange Asp.net problem. I have three pages:
Login. aspx: Enter the account password and save the account (YH: user) and permission (js_id: Role ID) as session
Authority. aspx: generate an XML treenodes File Based on the permissions saved in the session (js_id: Role ID ).
Left. aspx: Use Treeview to display the relevant navigation bar based on the permissions saved in the session. treenodesrc = "authority. aspx"

Directly call authority. aspx to display Normal XML files
Directly call left. aspx to display the normal function tree structure
Call login. aspx: Enter the account password, save the account and permissions as Session, and redirect to left. on the ASPX page, treenodesrc = "authority. aspx "(generate XML page), then in authority. aspx VBCodeThe session is lost, so that the obtained permissions are incorrect, and the function tree structure is incorrect.
The execution order of page_load on the three pages is as follows:
Login. aspx --> authority. aspx --> left. aspx
In login. aspx, left. the session value in aspx is correct, but authority. aspx session is reset, as if another session is re-enabled, but the original session is still valid.

For help: what is the problem and how to solve it? Thank you.