Re: Aurier - I agree that he's probably the one to point as a flop, in a similar way that Lamela was a flop during his first season. We expected a like-for-like replacement of a 2016-17 Walker in Aurier, and what we had was closer to a 2013-14 Walker: atheltic & speedy but rash in challenges and prone to brain-fart moments. However I'm not too worried about him like many of the comments above. Poch has a knack of getting the best out of fullbacks especially, and he will coach Aurier to be better at his game.
I'm more disappointed towards Rose, actually: he was so dominant and imperious last season, which adds to the fact that he's been country miles off the 2016-17 Rose we remember so fondly. His interview with the Sun has also soured many of our sentiment towards him, too (including mine). If Sessegnon does arrive, that would be the end of his time in a spurs shirt. Hoping for Fullham to be knocked out of the promotion playoffs..
Other than the two, can't think of a player who's played below expectation so much to be a flop in my book - a slight concern towards Wanyama & Lamela for their post-injury struggles, Winks for his reoccurring ankle injury, and Lloris for his gradual dip in his athleticism required for a sweeper keeper. Personally I didn't expect much out of Sissoko & Llorente from the beginning, so I won't call them flops; we'll need to move them on to upgrade our squad, though.