Query related to ARB order type

What is an ARB order type that are given by brokers??

This afternoon one of my bracket orders target was achieved, simulataneously the STOPLOSS order was also triggered and I was in a net sell position.

The broker also announced that all bracket and cover orders should be closed by 2pm or they will be auto squared.

Finally, the net sell position was still there and at 2:53pm, there is a ARB order type used to buy a similar quantity position.

So, there is a sell position (using bracket order type) and there is a buy position (using ARB order type).

Q1.) What is an ARB order type??

Q2.) Why did the broker not open the buy limit and buy STOPLOSS order when the order was initiated ???
(It was surely not a lack of liquidity reason, the stock in question is Adani Enterprises and the time of trigger of the order is around 11am, so there was ample of time)

Q3.) Is this a systems issue??
(Though end of the day the positions ended in a profit)

Thankfully, I keep two broker accounts with Zerodha and the other broker (whom I won’t name here).

I strongly urge the Indian stock broker association to please have good customer response service atleast on system based queries (not on trading queries).