Sacrificing of own units to spells with sacrifice does not count against the aim of 8 units.
Killing of own units with mass spells / abilities does not count.
Losing units due to opponent’s Meteorite does not count.
Losing units due to opponent’s red spells sometimes does count and sometimes does not.
Because the Rambler (opponent) is almost not damaging nor summoning creatures, the Sacrifice task (third) seems to be currently unpossible to meet.
It’s a bug, you have to actually kill your opponent’s creatures to complete the task.
Not anymore. It counts your own creatures now.
Just read the post about the undocumented fix. Sounds like it’s too fixed, now 
Where should I read what? I do not see any post with later date then I was posting this..?
Actually it still behaves like you said. So it counts only when the opponent’s creatures are destroyed.. well, good to know.
I’m confused I know for certain that the sacrifice objective from Liliana (chapter 1 part 1 story 8) actually counts your creatures.
A few days ago someone said in the forum how to easily beat those sacrifice/destroyer tasks and I tried it on that one.
Then I realized that it counts your own creatures (I’m sure because I just have beaten it a few minutes ago). So naturally I thought they must have fixed the sacrifice objectives.
But after reading your posts here I checked and yes other sacrifice objectives still count as destroyer missions.
Weird.
The Heroic fight against Nissa, #1 has Sacrifice 10 of your own creatures as it’s 3rd objective (for the 15 crystals). I can’t seem to make that number budge at all. It doesn’t count kills or my own creature deaths. I may need to take few months break from this game. There are so many bugs it’s just an exercise in frustration.