I always been wondering how Facebook engineers update the web interface for different users.
I always found the changes in the web interface very inconsistent: why do some users get some reactions (
, 
, etc) before others and why do some other users get it removed before others?
The same can be said for the new dark theme, for some reason i always get the reactions very late in their life cycle, while (AFAIK) i got the dark theme feature before a lot of my friends.
Some other times, though, I notice I don't get these feature at all (e.g. i never got the 
reaction).
I'm sure I'm not the only one that can observe this behaviour since at the time I'm writing the care reaction has been removed for a lot of people while I still maintain it in my interface.
Also, I'm sure this is not something related to your localization and it is done on a user-id basis.
My question is: Is this inconsistency derived from the distribute nature of Facebook data center? Is it something done on purpose depending on the user preferences?
Any insight will be very appreciated.
