I just left some gifts under a friend's tree (sending the last of them out right now, been slowly sprinkling them out all month) and JUST NOW did I get achievements... I've sent well over 25 gifts, but it only counted the ones I just left. Is this a bug that can be fixed? Should I make a ticket? Is there a way to fix it myself?

I also don't have the achievement where I put an ornament on my tree... even though I've used all 50 slots.

yeah the gift giver achievement was bugged for most of the month and only just started working, but not retroactively. personally i just sent a bunch of junk gifts to make up for all the real gifts i sent that didn't count.

if the ornament achievement isn't updating, you could probably get a UA to fix it by filing a ticket.