Today while playing I noticed that if you do the alliance quest for the Dragon, the cutscene which should play when you deliver the egg don´t play. The screen flick and then return to the game. All other cutscenes appear to play fine, I tried reloading but no change.

I can confirm this. When I deliver the egg to Deftclaw Redreaver, the cutscene starts and I can see a shade of the egg, but then the cutscence ends and I am back in the dragon leader's cave. Maybe the video file is damaged? There was also a problem with the soundtrack, that led to a crash, when you entered Escaton's Palace. I placed one of my classical music pieces into the soundtrack folder, renamed it to 1.mp3 and it worked. That way, you can import custom music at least.
I didn't find a solution for the dragons yet. Is there a way to access the cutscenes? If there is, I could try and look for a fix until the problem is adressed by the support.

I have the same problem. Just completed the dragonslayer alliance quest and the video didn't play. I use the GrayFace patch, tried different compatibility settings or changing registry settings but nothing helped. The intro movie plays fine and I don't know if the others do too as I haven't gotten there yet.
Edit: Actually, there was one before that when you bring the troll for the guildmaster in Alvar and that played fine. So I think those videos might be corrupted.

Sorry to bump this, but I'm having the same issue. All cutscenes seem to play fine, except these 2. Anyone has a solution?

I don't recall having this issue the last time I played, and I usually recruit the dragons. Maybe I just don't remember it happening. Try a reinstall?

Tried reinstalling. Didn't work.

Do you have the GOG or CD version?

I'm pretty certain I've got the CD version laying around, but if I have it currently installed, then it is almost certainly the GOG version installed. I'm not sure I even have it installed atm; but I believe I used the GOG version the last time I played.

I have the CD version installed - I might try to get to this point later and see if it's possible to reproduce the issue. There might even be a way to fix it.

Edit: yes, it plays in my version. Here's a recording:
https://youtu.be/3S61ig2DfZc

Edit 2: Forgot to mention that I'm using GrayFace MM8 Patch v1.4

Edit 3: Can confirm that after I installed the gog.com edition and copied the same savegame over, the cutscene does not play in that version. Seems like a bug in the gog.com version.

Edit 4: I took a look at the internal video files using St0rmCat's viewer and there doesn't seem to be any issue with the actual video file (dragonsrevenge.bik inside Magicdod.vid). It's most probably a bug introduced through one of the other modifications that gog.com has made to make MM8 work on modern machines. I'll raise a support request for it.

Here's a savegame which can be used to reproduce the issue - rename attached file to save012.7z then extract the savegame into Saves directory. After loading the game, walk forwards, press space to enter the cave, then select "Quest"

Edit: removed file, this post has a better one:
https://www.gog.com/forum/might_and_magic_series/mm8_prestarting_questions/post55

Got the following reply to my ticket:

Hello,

Thanks for clarifying. I've also checked the forum. This looks like a bug on our end and I will inform our product team about this issue, maybe they will be able to solve it. I'm sorry for current inconvenience.

Regards,
Dr Cat
Customer Support Representative
GOG.com

I had a similar reply - thanks Gog!

Hi, just bought the game, looks like the product team didn't solve this issue. Can we expect a fix one day ?

edit :

GrayFace's MM8Patch v2.3.1 solve this issue for me, I run the game with wine under arch linux.

kind regards