DoorDash Senior Monitoring Engineer interview questions

It was a lengthy interview process. 7 rounds..first you speak to a recruiter on the phone, then you do two interviews back to back(2 hours in total) with hiring manage and head of the team, then 4 individual interviews(1 hour each) with various members of the team. These 4 interviews include everything from system design, live coding etc after clmpleting all 7 rounds, didn’t respond for a months(said ppl were out for Christmas as it was Dec) and sent me a generic rejection email after putting so much time and effort into the process.