I have one particular NPC, the first one I made actually, that simply refuses to say any line which is the Branch opening line. You still have your responses, and he will vocally respond in kind to any of them. He just won't say his opening lines. Has anyone ever experienced this problem?
P.S If it wasn't clear, this doesn't happen with any other actors.

Did you set it as 'blocking'?

1) Check if the topic is Top-Level
2) Check the Priority (Default is 50)
3) Set the "start topic of branch" to that topic

I have not set it to blocking. Should I?

Both branches are top level, priority 50, and have the start topic set properly.

Blocking is to set the topic to replace the Greeting. Since this is usually the first line the person says, I thought that's what you're trying to accomplish.

No, what I mean is that I walk up to him, and it allows the player to initiate Dialogue with the line, Need a Favor?. The response in this topic is "Maybe, maybe not...". Then the next options are, "Piss off" and "I'm your lad."

Basically what happens is you walk up to him, say "Need a Favor?", there is a brief silence, and then "Piss off" and "I'm your lad" show up. The rest of his lines he speaks perfectly fine.

This pattern is there for all of his lines. It's really confusing me.

ahah. It looks like he's saying the lines, but you don't have force subtitles checked. (Or general subtitles turned off). Also make sure you made a blank sound file (and saved it )

Do you honestly think I didn't make sure I'd saved my sound files?

Oh, and I voiceact all of the characters.

I wasn't trying to insult you, it was small thing that I've missed many times and many others have too. It's definitely a facepalm moment - I'm just saying it happens.

If you want help, don't be rude to those helping...

Sorry, I guess I lashed out in frustration. But yeah, I re-recorded that line Many Many times. Won't work.