I really dunno, but it was a heck of a long shot to begin with, TBH. Ironically, a Franco-British alliance still emerging for TTL's *WWI in another universe would be more likely, and that required some pretty skillful diplomatic maneuvering, TBH, and I doubt a German Hanover would change all that much by itself outside of England proper(even if the butterflies afterwards might), as it was just a convenient second home for the Kings (and Queens) of Great Britain, more than anything.
Really, one could argue that it's honestly just one of the many oddities of real world history, like Courlandian Tobago[1], or the American Congo[2], Russian Yemen[3], or Mexican Guam[4].
Call me a fatalist if you like but all 5 of the examples you use are perfectly logical results of geopolitical ambitions.
Courland tried to settle Tobago because they were a trading based society attempting to get in on the highly profitable triangle trade. The Americans got the Congo because the main european powers didn't want each other to get it and so wanted a neutral power overseeing it that they could all trade with. Russia needed Yemen and it's agreement with the desert tribes there to guard it's colonies in eritrea and act as a protection for it's allies in Ethiopia and another threat to Ottoman Power. And Mexico's history as a country has long been based on the strength of it's navy, which is why so many islands in both the carribean and the pacific have come under it's protection, it's classic defence in depth. Taking Guam is a natural extension of taking Clipperton and Puerto Rico.
Same with Hanover, the existence of a german state in personal union with Great Britain was of course very convenient to the British Kings, who could use it to recruit private armies of germans, to train their sons in governance and keep influence on the continent. There's no reason for the British to abandon it, which is why they fought for it with such ferocity in the seven years war.
And the decision to form the United Kingdom of Great Britain, Ireland, Iceland and Hanover was a logical result of an attempt at centralisation in the aftermath of the irish jacobite revolts and the second english civil war.
So yes, I don't think you can write these off as just quirks. Each would need a deep change to the ambitions and aims of the governments in question to prevent.
And honestly if you do avoid them, then there isn't a first world war. The fact that the much vaunted united Germany didn't include the german speaking citizens of the UK, France, Denmark, and Austria was what led to the German-Russian-Italian Alliance in the first place.