I’ve been running into this issue with my game for a while now, and just got it fixed…
I Create a “Coin” from the server and parent it to a folder, then from the client I call .ChildAdded and animate said coin.
Though sometimes it throws an error:
I tried everything I know to fix the error, though one thing did not cross my mind, is that ChildAdded might of been called too early, before even the coin is properly parented…
Thanks to @einsteinK for thinking of that, 
Just seemed too silly for this to happen but… ya… now its fixed I’ve kept the game running for so far 10 minutes and the error did not occur at all and all coins are animated, [ before it usually happened in the first two minutes ]