You could try re-installing the app perhaps. On the iPhone I hit the + symbol on left to go to a larger reply window.
Then at bottom of my draft post I tap the icon with the mountains or clip (tbh not sure what clip does, seems the same as mountain icon I've seen before).
Then select best, medium or small photo (only gives original file size for me so that is a try and see).
Edit - then for some reason my photos are displaying twice (stored on two platforms?, so I delete one with an edit).
Sorry, anyone who got a heap of re-posts. Was just trying to see what the clip feature did differently (can't see anything?).