There is a bug with Beyond Reach, causing some NPCs from all over the game to (inconsistently) not talk to you.
This bug only affects generic NPCs (Those who have nothing to say outside of "Hm?", "Need Something?", "Yes?")

Examples
Some NPCs added by Dawn of Skyrim
Just about every NPC added by Populated Skyrim
A bunch of vanilla NPCs like Gwendolyn

If you were to spam-activate one of these NPCs while affected by this bug, they would simply stare at you and say nothing at all.
This was not very immersive to me, and with mods that added a lot of generic NPCs to the world, it made the world feel very robotic and dead.

It is not an issue that is reported a lot - in fact, it seems like I'm the first one who took an interest - but it is a very real problem, and there is a high probability that you encountered this, too.

Well, don't you worry. Drblaettchen's got your back! I have the solution right here!

Here's the how and why
The answer lies in the Quest record XX399EF2 - ArnimaLastKingVoiceQuest.
Unlike the other quests named ArnimaXXVoiceQuest, it does not have a Quest Dialogue Condition set.
Once set to check you're talking to the appropriate NPC, things work just as expected!
Generic NPCs will finally resume incredibly engaging and stimulating conversations with you again!

Truth be told, I am not 100% sure why it works. My best guess is that for some reason these NPCs are trying to access the quest dialogue but can't - so they're just mute instead. This is purely speculation on my part, based on the record I am editing to achieve my fix.