Middle-earth: Shadow of War was initially due for an August release, but that's now been delayed to October 10. Monolith Productions made the announcement today, though there was no specific reason given for the delay.
From Monolith:
Middle-earth: Shadow of War expands gameplay in every dimension, including the massive open world, the story, the RPG systems, and personal player stories of the Nemesis System. As with Middle-earth: Shadow of Mordor, Monolith is committed to delivering the highest quality experience. In order to do this, we have made the difficult decision to move our launch date to ensure that Middle-earth: Shadow of War will deliver on that promise.
Monolith is quick to note that this date does not apply to some territories like Australia, New Zealand, and Japan — each of which will have different release dates.
On its face, it's likely that the delay is just to ensure some extra spit and polish is applied to the game before release. We saw something similar with Final Fantasy XV in 2016, which ended up being delayed by two months not long before it was to be released.
Of course, given the fact that it has already been confirmed that Shadow of War is "coming to Project Scorpio", speculation might lead one to assume the delay is to more closely line up with the next Xbox's holiday launch. There's no way to know for now, but we're expecting to learn of Scorpio's release date at E3 later in June, so we'll know soon enough.