To ensure that they aren't liable to HackerRank for any infringing content, GitHub has to keep content down for at least 10 days after receiving a counter notification.

Do you plan to contact GitHub and give them a legally binding agreement to indemnify them for any infringement of HackerRank's copyright in the material they took down (I'm sure there is no such infringement, but by agreeing you won't sue GitHub for restoring the content, you effectively retract the notice and give them no reason to wait the 10 days)?

I think a sincere apology should include steps to urgently minimise the ongoing damage to the existing victims, not just analyse what went wrong to prevent hurting other victims.