Why is the previous close price different from current open price

Alpaca Market Data
1

Hello,

I am experimenting with bars and I noticed that in my minute bars, the open price for one was different from the previous minute’s close price.
Does anyone know why?

Thanks!

2

Nonliquid asset and the market gapped would be my guess.

3

actually there is no such things as close or open price.
it is becoming more and more useless to check open/close.
if you check different data providers, you will see different OHLC prices.
there is after-market hours, and premarket hours.
and some brokers allow you to trade 24hr.s.