Bami's Cinder and Sunfire should stack
The decision to give Cinder and Sunfire the exact same Unique Passive means if you buy Cinder, you can no longer buy Sunfire (as it will literally have no passive anymore). Tank itemization is already crummy and damage is poor, so I have no damn idea who thought it was a good idea to give a tank jungler 1 less item to buy unless they sell Bami later (given it's 25% health bonus, that's really not going to happen).
Is this just to stop champs like Jarvan/Vi/Lee from stacking both then tons of damage as they already do? 'Cause having a better jungle tank item at the cost of no longer being able to use a key tank item is just.... it's one step forward two steps back.
The closest comparison I can think of being blocked from using Hourglass because you bought Banshee's Viel already.
TLDR: You're buffing and nerfing tanks in the same patch by making Cinder invalidate Sunfire completely