system
A chat on subreddit /r/wallstreetbets
human
Extremely rare but possible if it's a low volume ticker. Robinhood definitely does put you way behind the queue for orders. 
  
 That's assuming if it hits your limit target and then shoots above past it. If it goes below your limit target you 100% had your order filled.

gpt
It's not extremely rare on RH. It's very common. RH orders don't go directly to exchanges, they go to market makers and HFT customers first.