Dumb question about limit and sell orders

So I've been doing limit and sell orders fairly often on robinhood for the past 6 months without any issue. They've always gone through immediately without hesitation, it seemed like a flawless system. I get my exact prices, no fees like market order/sell. Anyway last night I put in my limit order like usual, the price dropped to my limit and no sell was triggered. It continued to drop, still nothing. I canceled the order and placed it again later for a different amount. Same thing happened. I was going to just go ahead and do a market order, but the fee was around $500. I just don't understand why it has worked all this time until last night.