Having rewatched it I definitely think it's the opening part that sets off the strange vibes.
The fact it's silent, the glances between the sister and brother. Is the son sulking because Dad hasn't opened his present (in which case it paints a bit of a weird picture where nobody feels comfortable to say 'oi, Dad you missed one') or has there been a fight etc.
Maybe that is some of us projecting based on our previous experiences but there have been a few comments about people feeling unsettled/uncomfortable. If you've been in a family environment where a parent is volatile there's some shades of that at the beginning.
I think it works better if you skip the first few seconds and it starts with Dad finding the present. You still get that connection between Dad and son based on music but you haven't potentially triggered some of your audience. It's a stronger advert for me if it starts with the son coming downstairs and realising that his Dad has found the gift.
It's nice to do something different than breathy cover/perfect happy families at Christmas and we're all talking about it so from an advertising point of view it's done it's job!