The most common report of this is with Runaway Gyrocopter ("Deathrattle: Deal 5 damage to all enemy minions, then shuffle this into your deck.") in adventure mode when a Deathrattle doubling effect is in play:
The issue seems to be due to the rule that the first "cheat death"-like effect decides where the minion ends up. Specifically, it's apparently implemented as "create a copy of this in the specified zone, and suppress any subsequent cheat death effects for this death." Faking it like this gives the appearance that only a single card exists, but it can cause any side effects like Pyros' transformation and Gyrocopter's AoE damage to be suppressed as well.
This was touched on in #1064, though Anub'arak is known to be a bit of a special case among "cheat death" effects, and did not exhibit the issue with Cheat Death (the actual card).
The most common report of this is with Runaway Gyrocopter ("Deathrattle: Deal 5 damage to all enemy minions, then shuffle this into your deck.") in adventure mode when a Deathrattle doubling effect is in play:
https://us.forums.blizzard.com/en/hearthstone/t/bug-with-runaway-gyrocopter-necromechanic/16917
https://www.reddit.com/r/hearthstone/comments/dv13xv/weird_stuff_going_on_in_the_single_player_mode/
However, a more generalized version of the issue can be seen with this old interaction between Cheat Death and Pyros: https://www.reddit.com/r/hearthstone/comments/aha35p/maybe_im_being_dumb_but_why_didnt_this_pyros/
The issue seems to be due to the rule that the first "cheat death"-like effect decides where the minion ends up. Specifically, it's apparently implemented as "create a copy of this in the specified zone, and suppress any subsequent cheat death effects for this death." Faking it like this gives the appearance that only a single card exists, but it can cause any side effects like Pyros' transformation and Gyrocopter's AoE damage to be suppressed as well.
This was touched on in #1064, though Anub'arak is known to be a bit of a special case among "cheat death" effects, and did not exhibit the issue with Cheat Death (the actual card).