I see on the video what appears to be a lot of flap extension and was thinking of high drag during that flight, especially once the airspeed was bled off.
Yes - and/or raised them once in the climbing bank, just when the speed/AoA/lift equation would have been most critical (video is too low-rez at that point to be sure).
But there are a lot of other and/ors in this complex aircraft that gets 161 kts out of 100 hp/75Kw-h. Prop lever not moved to high rpm, confusion of flap and gear levers (different, but close together), or indeed an engine issue.