1.) The purchased shares may be short-delivered.

Ideally, when the shares are purchased, they are settled on T+1 day. Now, if the shares are short-delivered, it means that the seller of the shares defaulted on the settlement of shares. In such cases, the exchange holds an auction for the same quantity of shares and delivers it to the buyer and will appear in the holdings on T+2 instead of T+1. In such cases, Tradejini notifies the clients via email. 

2.) A Stock which is under Trade to Trade (T2T) series may be sold and bought back

Trade-to-trade stocks are not netted off in case of intraday square off. Hence If a T2T stock is sold from the holdings and bought back on the same day, then the stock won’t be visible in the holdings until it is settled i.e. on T+1 as the sale will result in delivery debit and the purchase will result in separate delivery credit and will be treated as 2 independent transactions.