Do you see the "Write a comment" field but when you click on it, the field does not raise up, it stays under the virtual keyboard and nothing happens when you type ? (happened to me after an update on a LG G6)
Dont worry, nothing is broken, you just have to open the phone nav bar and click on that new button on the bottom left :
This will toggle the "lock mode" of the nav bar and will fix your problem !
Happy commenting ! :)