Does the embargo affect any reviews that give an overly positive reception? Did those get to release early without consequence?

No, not usually. Embargoes are usually across the board in that you can't release a review ahead of what they say even if you give it a perfect score. The thing is, embargoes aren't really legally binding if both parties don't really sign anything. When you get a review copy with an embargo, it usually just has a slip of paper that says you can't put a review up before such and such a date and time. You could but you don't want to because chances are that the publisher will not give you any more review copies in the future. I don't believe there's much of a risk of legal repercussions for breaking the suggested embargo date. I don't think there is, but I and most every other outlet would rather not risk it just in case.

"Early" reviews from some outlets are typically due to an agreement made between the publisher and the outlet ahead of time. Now, whether or not those have stipulations about how they must score a game higher than x out of y, or if money exchanges hands behind closed doors, I honestly do not know.

Other "early" reviews can come from media outlets that were not provided a review copy ahead of time but instead bought the game. I mean, you can't really stop someone from reviewing a game early that they purchased with their own money from a store that sold the game ahead of schedule. Which is why these launch day or post-launch review embargoes are absolute nonsense.

These late review embargoes step into anti consumer territory, a lot of consumers want to know what they are buying before buying it, Ubisoft are just hoping people cave in and buy it before seeing anything which might put them off picking up a copy.
It might not even be because there seems to be a few issues with the game at the moment, this is probably just a businessman decision someone made regardless of the game's quality.

Whatever the decisions behind it, it shows zero trust from Ubi towards its community including reviewers.

I see. Thank you for the very clear explanation Zips. I'm also facepalming VERY HARD at the fact that I could've clicked on the links you've given us to answer the question (like Kotaku for instance). My bad for not reading/listening and getting the answer there. But I do appreciate you helping us understand how embargoes work, and why journalists honor them.

I thought publishers have ways to shut down an article due to breaking embargoes, but I now know this isn't the case. It's more of a threat that they won't offer anymore games, events, or other opportunities, which damages your business as a result of not honoring the embargo after receiving anything to report on for the publisher's product/service.