Gaps (the difference between the close and open prices of two consecutive periods) between two days can be understood by the many events that may happen between the market closing and the market opening. However, what can explain gaps in a one-minute time frame of an intraday chart?
The right side of your chart depicts trading during regular hours on 12/02. There's a candle every minute because the security is being traded actively.
The left side of the chart depicts trading during the after market on 12/01 and the pre-market on 12/02. Liquidity is low during after extended hours trading and if a trade doesn't occur during a one minute time frame, there is no candle.