landscape pages changes to portrait page automatically without changing the setting. why?

when a landscape page is selected between portrait pages , the landscape pages converted to portrait when the libre office writer open everytime. why?

Read these guidelines and ask a good question. In particular, specify the file format and share a sample file demonstrating the problem (modify your original question or add a comment).

Did you insert manual breaks between your portrait/landscape pages? These manual breaks allow to choose the page style to apply after the break.