As of today, Bethesda released Skyrim patch 1.6.89.0.1 to the public. Unfortunately, this patch introduces a new, and severe, bug concerning dialogue.

Any mod that attempts to edit any vanilla dialogue will break the dialogue topic and cause it to lose its connection to its voice and lip-sync assets. This causes the dialogue in-game to become silent, with no voiceover and no lip-sync. You have to turn on the subtitles to get what is being said. The dialogue will also lose their connections to their result scripts, which means THIS BUG IS GAME-BREAKING. And because of that, I feel this bug deserves its own discussion thread because it is on par with the late NavMesh bug concerning how badly it can affect your game.

If you wish to discuss the Edited Dialogue Bug and its implications for modding, please do so here.

A Creation Kit update is expected at some point because 1.6 introduced a new sub-record to Update.ESM that our versions of the Creation Kit are not yet aware of, and we can hope it will include a fix for this bug, as well. But until then, awareness of this bug throughout the community is paramount.

Can you give any more details about what exact behaviors trigger this? I assume from your wording that editing the text of vanilla dialogue is a sure problem. What about adding conditions to existing infos? Or adding new infos to a vanilla topic?

Thank you for identifying this serious issue and bringing it to our/Bethesda's attention.

So far, it appears any edits made to any vanilla dialogue topic whatsoever causes this to occur. The trigger is simply that a record for the dialogue exists in your plugin.

Here is my take on this.

Another user mentioned that Bethesda seemed to have implemented a new silent voice system to the dialogue. I tested this and confirmed it. Dialogue no longer flashes by, but instead stays on screen for 5-10 seconds, long enough for the player to read. I think that this would be an excellent mechanic, especially for modders who prefer not to use voiced dialogue or simply do not have voice actors to do so. But unfortunately, I believe that this new system has a lot in common with this dialogue bug.

Think about it. This silent voice system is introduced, and then suddenly we get a game-breaking dialogue bug. It's just too much of a coincidence. Maybe the new system thinks that edited dialogue is instead new dialogue altogether, and thus searches for the audio and lip sync in the wrong place. Or maybe the silent voice system simply takes priority over any user dialogue, whether edited or created. We can't know for certain until Bethesda recognizes this.

That's my theory about this bug. Whether or not those are the reasons this bug happens, I definitely think that the bug has something to do with this new silent voice system.

Interesting, and given what other users are saying, there is a new silent dialogue system in place. I would not put it past them that this bug is the result of a programming error in that feature.