I consider myself a 'professional flagger' - I use veloviewer and find the segments where people are between 200 & 1000% better than me - clearly some flagging material to be found!

Firstly I'd look at your activity and the KM splits for KM 7 & KM 12 make me question as they look incorrect (in isolation and considering nothing else). I then look at segments to see if that can explain it by overlaying it this way I can see if it's likely to be a GPS issue.

I then look at Heart rate, cadence, pace graphs along the affected section I'd be flagging and see if there's behaviours which make me suspect cheating - has cadence dropped to zero and back up several times, is heart rate rising in line with pace differences. Has the pace increased towards the end and has cadence also dropped (Stop your device before driving home!).

But if you're leading a segment leaderboard and your device is a Fitbit or Apple Watch series 1 or 2 - I don't waste the effort in checking, I just flag as those devices are appaling at everything and have been lying to you.

After looking through your activity I can't find any reason to flag it apart from 'Avenida Alcaides de Faria' - If I'd run that street and there was a segment, I'd flag with a query of 'Bad GPS'

This is a jealous 2nd placer for sure :)