Is the wrong version installed? Run npm i --production to ensure the proper composer version is installed.
Otherwise, perhaps the issue has been fixed in a newer version of NodeBB... what commit are you on?
I am using 'Persona' theme and have an issue with 'Reply' button. Currently, when I hit that button, it triggers a modal 'Create a new topic instead?' with 2 buttons to reply the topic or create a new topic.
I don't want this behaviour. Instead, I like the Reply button to open the composer.
That modal shows up if you try to reply to a topic that is too old, this is a setting in the ACP. Look for "Days until topic is considered stale"