Quick Reply buttons may not be displayed correctly in Instagram on Android devices right now. We have reported this issue to Meta here: https://developers.facebook.com/support/bugs/1402012250298307/ - please check this bug thread to keep track of the fixing process.
Please note that if you exit the conversation and re-enter it right away, Quick Replies should appear correctly then.
We will update this incident as soon as we have any updates on the subject.