I discovered the same problem today in InDesign 2019 on macOS Mojave 10.14.4. This feature has been working for years in previous versions of InDesign just fine. In the 2019 version, whenever I try to make a pdf of the imposed booklet, the "preview" looks correct but when the resulting .ps file is converted to a PDF, the pages are portrait orientation and the content is chopped off.
I discovered the same problem today in InDesign 2019 on macOS Mojave 10.14.4. This feature has been working for years in previous versions of InDesign just fine. In the 2019 version, whenever I try to make a pdf of the imposed booklet, the "preview" looks correct but when the resulting .ps file is converted to a PDF, the pages are portrait orientation and the content is chopped off.