It comes after a flood of racist abuse was directed at England footballers Bukayo Saka, Marcus Rashford and Jadon Sancho following the men's Euro 2020 final.
Instagram boss Adam Mosseri said content had "mistakenly" been identified as within guidelines instead of referred to human moderators.
The issue had now been fixed, he said.
“We have technology to try and prioritise reports and we were mistakenly marking some of these as benign comments, which they are absolutely not,” he told BBC News.
“The issue has since been addressed.
"Reports on these types of comments should [now] be reviewed properly.”
On Monday, BBC News reported a comment containing several orangutan emojis on Saka’s Instagram.
Within minutes, a notification was received saying the platform’s technology “found that this comment probably doesn’t go against our guidelines”.
BBC News requested a further review but received no response.
On Thursday, Saka himself responded to the abuse.
"To the social media platforms... I don't want any child or adult to have to receive the hateful and hurtful messages that me, Marcus and Jadon have received this week," he wrote.
"I knew instantly the kind of hate that I was about to receive and that is a sad reality that your powerful platforms are not doing enough to stop these messages."
Following Mr Mosseri’s comments, on Wednesday night, several more racist comments and emojis were reported - but no notification of the results of any review was received.
A quick scroll on Saka's account reveals plenty more racist comments yet to be reported and removed.