Couple things to try.
Stop nodebb and run ./nodebb build and try again.
Also run ./nodebb plugins to check active plugins and see if persona is active.
When creating a new topic on a mobile browser, the input field disappears so you can't see what you type. This is because, other than replying to a topic, the category list is shown.
Is there a quick fix for this as the most users of my forum are using mobile devices to creat/reply to topics.