As suggested by people on this thread, I followed what they suggested to fix Miraak's script and it did indeed work, which suggests that the previous theory about the DLC being downloaded before the patch is to blame for breaking Miraaks encounters.
1) Uninstall Patch
2) Uninstall Dragonborn DLC
3) Clear Xbox System Cache
4) Re-installed Patch
5) Loaded up Skyrim, and loaded your last save and agree to losing any items you may have previously acquired during the Dragonborn DLC.
6) Save the game, thus creating a 'Clean Save' meaning it has no Dragonborn progress on it, but has you're newly re-installed patch
7) Download the Dragonborn DLC
8) Finally Blast though the entire main quest line in a couple of hours, WITHOUT EXPLORING! and hopefully experience Miraak steal a dragon soul from you after you read the first black book in Solsthiem.
I know this is a terrible fix and essentially means you'll lose all progress you may have made in Dragonborn that isn't related to any skill level ups, BUT if you're like me you already saw everything worth seeing and can thus skip the dialogue and sprint around to wherever you need to go, and it doesn't take nearly as long to get back to were you where as you would imagine. However this is still a serious issue that needs patching as I can see a lot of people returning to Skyrim for this DLC and falling victim to the same series of events related to DOWNLOADING THE DLC BEFORE THE NEWEST PATCH as we all have.
####-ORIGINAL POST-####
Well I have been hanging around these forums for a little while now trying to gauge how many people have been experiencing the same game breaking Miraak turning ethereal glitch as me. Firstly from what I seen there are two variations of this glitch.
1)You break the games script by killing him too quickly and thus HE ABSORBS THE FIRST DRAGON SOUL and ends up getting stuck since he can’t consume another quick enough
OR
2)You break the games script by killing him normally, but end up ABSORBING THE DRAGON SOUL YOURSELF, thus getting him stuck from not completing the act.
Now, I’m not certain but the first one, seems to be easily addressed by simply slowing down the beating you are giving him, whilst the second one isn't so easily addressed. If you are experiencing the second version of the glitch and “YOU END UP ABSORBING THE DRAGONSOUL”. I have noticed some patterns in player experience which has now lead to the formulation of this hypothesis about what may be causing it.
A few people who also have this glitch also say they did the same thing as me, and DOWNLOADED DRAGONBORN BEFORE THE LATEST PATCH which has lead me to believing this may be the cause. So, for people who are experiencing the same game breaking glitch, I would like you to say if you did the following same five steps whilst playing Dragonborn as me, which should hopefully provide further evidence that either proves, or refutes it.
Are you experiencing the glitch after carrying out these 5 steps? Alternatively did you not experience this glitch after carrying out these five steps?
1) Downloading Dragonborn from marketplace
2) Start Skyrim up and be prompted to download latest patch
3) Load up a previous saved game in Skyrim, then realize you can't start the DLC and be forced to reset and reload
4) Start playing though the DLC normally and not experience Miraak appearing to steal a dragon soul you earned from killing a dragon on Solstiem.
5) Finally take part in the final battle with Miraak and experience the ethereal glitch caused by you getting the dragon souls and not him.
Hopefully, if this receives enough evidence, it may increase the speed of a fix or provide some inspiration for a workaround that actually works.