Reposting, as my previous post has been taken down, for alleged TOS breaking. I've dug up my every old, beat up phone, to prove you moral sheriffs wrong (thanks guys, you're really making the world a better place! /s).
As per the actual post:
I haven't seen this mentioned yet, so this is to warn you of a potential bug. While claiming rewards for completing weekly challenge, do not press skip! As I can't think of any other potential cause, I assume skipping the animation caused de-sync of friendship levels between player A and remaining 3 players, taking part in the challenge. Refreshing game data, further interactions, nor simply waiting for two days now, do not force the levels to sync, so I'll just observe what happens, when final "heart" is reached.
by RayD64