I dont think it has anything to do with layers as same issue on Mankrik/Pagle cluster and we have been on one layer only since HC launch. The extra layer thing is a red herring unfortunately , as it is just vestigial information of the old overworld zone id instance in Nova from the reset yesterday (it is there until the addon cannot detect the NPC resets on that layer, then it knows to remove it).
However, i was also in BB for that drop and some people right beside me would get it and others would not. Blizz devs please take a look into if this is only being applied to people from the server of the heart dropper, maybe another clustering issue? This is kinda game breaking for raiding community in Era.