Meta SWE, ML - E4 , rejected after final loop

Phone Screen

1. A slight variation of moving averages
2. A slight varitaion of find the peak element

Loop

1. Behavioral - usual questions, they asked a lot of questions to me, almost for 40 mins
2. Coding round 1 -
   a. Make valid paranthesis - remove one cahr, follow-up - remove "n" chars (they didnt want the code for follow-up but just what i would have done and why)
   b. Given a list of intervals, find the number which is contained by maximum intervals
   [[2,13], [3,5], [1,4], [2,5]] -> answer should be 3 as it is contained by 4 intervals
   gave a greedy approach. then a subotimal o(n^2) approach, coded the suboptimal
3. Coding round 2 -
   a. merge sorted array without duplicates
   b. lowest common ancestor
4. ML system desgin - design a location recommendation system

Gave my best shot, the interviewers in the 1st three rounds were happy and said, good job/great job, but didnt do quite well in the ML sys design. So my guess is that was the round which led to a rejection. Did not get a detailed feedback from the recruiter. Best of luck everyone out there! If anyone would be so kind to tag the relevant link in the comments it would be appreciated, thanks!