I usually don't feel that 'conflicting happiness'. I only feel emotional torment/sense of defeat. The only difference between what I feel and your other examples is that one belong in the more tragic category (usually war stories, lots of fighting, etc, and thus no redeeming features). Its almost like nitpicking between a cup half full / cup half empty kind of situation but in my case I see something like "small cup 9/10th empty while dying of thirst" for these so called 'bittersweet ending'.
One example is having all your favorite characters die while the ones you don't care that much about obtain 'redemption' or w/e. On a side note, it is probably a severely biased view since my favorite characters are the ones that usually get killed off
(or getting killed off via zombification, thank you Gakkou Gurashi).
(Sorry. I think this is me venting a little about how my favorite characters get killed off or something every 2-3 stories. Starting to think I am a death flag. 😨)