Test image here.
For me personally when I want to upload an image I need to press picture icon, then upload. Then from there looking through my images I can't just select the one I want as that will not actually do anything. I have to tap and hold on the desired picture. That then brings up a larger version with an "add" button underneath.
Tapping add will bring me back to the previous screen and then I need to wait a minute for the image URL to be filled into the box once it has been uploaded. There is no indication it is being uploaded. Sometimes I'll wait for a couple of minutes and nothing will happen so I go through the previous steps again.
Then once the URL is filled on my reply, previewing the post will often not display the image to me for another up to 5 minutes. There is just blank space and no indication there should be an image loading within the preview.
I'm not sure if any of this makes any difference to you but I have noticed picture posting is a little funky and some of my experience may help you get more results.