I got call from hr and had around 5 technical rounds. Questions were easy n mostly on data structures Interviewers are very friendly,they give brief description about company and work before every interview

HR scheduled a phone screening interview with one of the engineer. Interviewer asked about current company , role and day-to-day activities and then briefed about role/team which I was being interviewed for. Interviewer quickly moved onto coding round. Question was to group anagrams from given list of words. I quickly briefed my approach ( hash tables) and started coding in Python. I could successfully execute the program with desired output. Interviewer asked about time complexity , corner/stress cases for given problem. I was able to answer all questions related to coding problem and interviewer looked convinced too. A day later , HR mailed me stating that she received negative feedback from interviewer and they decided not pursue any further. This entire episode baffles me till date.