Stop orders executed before reaching stop price

I placed three oco orders and at different times with different proffit and stop loss prices.
At te same time, all three of the stop orders executed with the same price which was higher than the stop price but lower than the proffit price.
Why did the system made that decition?

no broker can guarantee any bracket/OCO order to be executed exactly at the levels you put.
bracket order is converted to market order as soon as bracket’s upper or lower is hit.
market order is executed with a few seconds/minutes delay depending on the quality/speed of your broker.

I understand that, but the price was way to far from both the profit price and the stop price. Here is the information.
Order 1: Limit SELL: 120.15; Stop SELL: 115.55
Order 2: Limit SELL: 120.54; Stop SELL: 117.53
Order 3: Limit SELL: 120.02; Stop SELL: 118.02

Order 1 STOP Sell was filled at 119.90
Order 2 and 3 STOP Sell was filled at 119.89

I have seen worse!

Order 1: Limit SELL: 120.15; Stop SELL: 115.55
Order 1 STOP Sell was filled at 119.90

it was supposed to be filled at 115.55, but there is slippage of 3.8%
119.9 - 115.55>>> 3.8%

you may expect up to 5%, sometimes even more, again depends on time of the trading (morning is more volatile), or quality of your broker.