Does not affect Reborn. Cases shown include Electra + Sap and Brann + Blackjack Stunner. Could possibly do this with a Spirit of the Shark + Kidnapper, Electra + Shadowstep if you used some shenanigans to fill your hand before the spell resolved, and maybe even Commander Rhyssa + Freezing Trap?
As for why this happens, full zone instant removal (#107) is certainly one factor, meaning the minion is removed from play sent to the graveyard before the death phase. Normally that causes the Deathrattle to queue up for the next death phase, which would normally be after the second casting is done. So the second casting resolves while the minion is in the graveyard. Sapping a minion in the graveyard will ordinarily work, fishing it out of the zone and sending it back to the hand. But if the hand is full, the minion will instead have to be destroyed again. This is probably what causes the scheduled Deathrattle to be cancelled. It was previously thought that destroying a minion in the graveyard has no effect, but it seems that such is not entirely the case.
It's possible that this issue is related to #1064, another issue with Deathrattles failing to trigger on minions in unusual zones. Unsure if that still happens, or what common ground might be viable to explore, though.
Shown here: https://www.bilibili.com/video/BV1cA411t72p at 1:04 And here: https://www.youtube.com/watch?v=QBalhp31bks&t=1m43s
Does not affect Reborn. Cases shown include Electra + Sap and Brann + Blackjack Stunner. Could possibly do this with a Spirit of the Shark + Kidnapper, Electra + Shadowstep if you used some shenanigans to fill your hand before the spell resolved, and maybe even Commander Rhyssa + Freezing Trap?
As for why this happens, full zone instant removal (#107) is certainly one factor, meaning the minion is removed from play sent to the graveyard before the death phase. Normally that causes the Deathrattle to queue up for the next death phase, which would normally be after the second casting is done. So the second casting resolves while the minion is in the graveyard. Sapping a minion in the graveyard will ordinarily work, fishing it out of the zone and sending it back to the hand. But if the hand is full, the minion will instead have to be destroyed again. This is probably what causes the scheduled Deathrattle to be cancelled. It was previously thought that destroying a minion in the graveyard has no effect, but it seems that such is not entirely the case.
It's possible that this issue is related to #1064, another issue with Deathrattles failing to trigger on minions in unusual zones. Unsure if that still happens, or what common ground might be viable to explore, though.