Why was PV Sindhu given yellow card at World C'ships final?

PV Sindhu was shown a yellow card by the umpire for "deliberately causing delay" during the third game of her Badminton World Championships final match. Sindhu had earlier received multiple warnings for not returning to court when asked to by the umpire. Notably, two yellow cards in badminton lead to a red card, for which the opponent gets a point.