I try playing Kaya, but both her first ability and Grafdigger’s Cage seem to work against me, because cards in my opponent’s Exile disappear (without any cards being played with this or a similar effect) every other turn, so her third ability only deals damage for cards exiled during the preceding turn which is almost nothing. This makes her really weak and should not be as intended.
What was the opponent, and maybe there was some effect in play that affected opponent’s exile?
It was a lvl 30 Brokhan, but I don’t think there was any effect in play. It is also not consistent, I have matches where everything is fine and then (apparently random) it does not work. Maybe I am missing something major so I thought I post it here in case someone might be able to explain it to me 
Hmm - this is really odd. I was gonna suggest maybe golos, but he adds as many cards as he takes from exiles, so I got nothin. i play with her a lot and have never had this problem, so I’m very curious what’s going on here. If you listed the deck you’ve been using, we might be able to detect something funky? You’re saying you’ve had this issue in multiple games against different walkers?
Side note, for what it’s worth - grafdigger’s will actually always work against you a bit in a kaya deck, because it’ll exile your graveyard as well, instead of being able to use your ult to add it to opponent’s exile for extra damage.
I know about Grafdigger’s downside, but I am just leveling her (23 atm) so I try to get her ult out sooner rather than to dish out a little more dmg.
This is my current deck, nothing fancy.
Temple of Silence
Grafdigger’s Cage
Sorin’s Vanguard
Orzhov Racketeers
Imperious Oligarch
Angel of Vitality
Absorb
Infinite Obliteration
Undercity’s Embrace
Vicious Rumours
This issue seems to be resolved in 4.0 version.
Thank you for the feedback!