Hello,
When shares are sold from your demat account, you have to first confirm on the Holdings page if the holdings quantity has been debited.
If it is debited, then this indicates that your holdings have been sold at your selling price.
If you are on the Positions page, you have to confirm if your Position was sold under product type CNC. If yes, then your holdings have already been sold at your selling price. You can ignore the fluctuation in the PNL on the Positions page for your Sold CNC shares as this is irrelevant to you.
As for why we allow the PNL to fluctuate in the Positions page even for CNC trades, here is why. Several traders use their Holdings value as margin to execute intraday trades. This can be achieved by selling Holdings, using the instant cash credit in the trading account to execute intraday trades and then buying the sold Holdings back before market closes. Traders keep their Holdings intact at the end of the day because there are no capital gain taxes on investments held for over a year.
Showing such CNC sell trades in positions makes it easier for traders to see the MTM profit/losses on their Holdings Sell position before they buy it back.