I believe I am having a similar problem but with an android tablet.
The Facebook app was originally designed for a phone. So it has one column of information. When you turn your phone or tablet to landscape orientation, the app rotates but still has only one really fat column, very annoying on a tablet. A couple of months ago, I got a message saying that from then on, I would be viewing Facebook in landscape mode. The app then had multiple columns so that the main column with pictures, videos, posts, etc. was no longer too wide, and a second column with ads, chats, etc. It was a welcome change.
For some reason, when I logged on last night, the app had reverted to its prior single column or (portrait mode) state. I can't find any way to get my lovely multi-column display back.
Please Help
Roy