There's nothing really particular in your quest according to your video.
Instead of testing in a savegame, just COC in the main menu. Does your quest work ?
Then, one thing that could fail for your dialog when you test with a savegame is the condition
getStage yourquest < 10
Can you check in-game that what stage you're at in your savegame ? load your save and in the console :
ShowQuestVars QuestID
Maybe you have some remainder of a previous testing.
My dialog is working but I hit the dialogue missing problem when I make one to many aliases that influence vanilla NPC's. I made a post about this earlier. Need to test more to be sure if referencing vanilla npcs is part of the problem.
Same thing here, in the console type
ShowQuestVars QuestID
and check that you don't have an alias set to NONE.
NONE can be a correct value (e.g. if you have an alias initially disabled) but probably not for your case.
So it means the alias failed to get set.
If you're aliasing a vanilla NPC, chances are that the unique actor is already aliased by another quest currently running.
Go back to your quest alias and check "Optional" and "allow reserved". "Optional" avoids a quest failure when the alias fails to be set ; "allow reserved" allows you to alias an actor reserved by another quest.
Lastly, when it comes to aliases, it's always good to test with a savegame AND to test by just COC-ing in the main menu (this is a fresh game).
If you test with a savegame, you can have problems if the aliases settings have been changed and if the quest is already enabled (which will be the case if "start enabled" is checked on the quest). In this situation I would suggest to use COC on the main menu or to use a savegame that wasn't using your mod yet.
Alternatively, if the quest is not "start enabled" and starts with a given event (hooked in the story manager), you can also get back to a savegame BEFORE you started the quest.