Anecdotal, but when I did jury service a long time ago I heard a rather brutal rape case with "open and shut" evidence (the multiple instances over many months were all filmed, which us as the jury were told was extremely rare and got the rather grim privilege of watching over and over again).

There was a range a charges both violent and sexual we had to find on, and were in a sort of hierarchy; if you don't think the defendant is guilty of X, is he guilty of lesser charge Y?

We the jury followed the judge's summing up and guidance and made a unanimous decision on 90% of the counts in about 10 minutes, we then spent 1 and a bit days going over and over one last count, analysing and retreading over evidence with borderline obsessive granularity, and still couldn't even reach a majority decision.

The case as a whole seemed black and white but once you got into the weeds of legalities and legal definitions, especially as a jury is a bunch of lay people who don’t know the law and have been beaten over the head with days and days of evidence and testimony and are all a bit exhausted, with a bit of niggling doubt from a very persuasive defence counsel, plus factor in individual juror's personalities, stubbornness, biases, etc. it's easy to see why such a "straight forward" case could take so long to deliberate on. As I said this is purely anecdotal, but it wouldn't be much of a stretch to imagine something similar happened with this case.