Why aren't thumbnails of pages are not showing preview with master applied?

Please make sure Master is applied on pages where you are checking for master contents.

Master page contents should be shown in child pages if its applied to that page.

Also let me know which content you have placed in master which is not showing up in child page , is it all contents or any specific content , with all child pages or certain page ?

Upload few screenshots of plan layout and master page.

Thanks,

Sanjit

Perhaps you should click onto "thumbnail" in the upper right of the "plan" window.

I think the child page height is much more than master page which can be the reason here.

Can you check by keeping both Master and Child with same page height ?

Thanks,

Sanjit