Meta Developer interview questions

After submitting my resume and answering a few questions on past projects, job preferences, etc. I had two Skype interviews on algorithmic questions. The problems posed were quite fair and had to be solved in a programming language of choice in an online editor. After that, I was invited to an on-site interview in London (expenses paid) with three more one on one interviews. Two of them were once more on coding, this time on a white board. The other one also had a small coding part but also included questions on previous projects, team behavior etc.

Met recruiter at the Facebook offices, she showed me around. Because I was applying for an engineering position, it started on the engineering floor, which isn't too big. Nice offices but nothing super special, she did mention they were moving fairly soon. After the brief tour went down to the 2nd floor and went to a small room for the technical screen. An engineer came in and for a minute or two asked me about my background and work experience. Then went and asked me two technical questions. The first one was pretty straight forward, but I spent a long time explaining my thought process and debugging and everything. (As a ton of sites say you do). Second one was a bit more of a puzzle question and stumbled a little on it, basically it was a binary search algorithm. Unfortunately a miscommunication at the beginning of the question caused me to try to think of it in a different direction, but eventually got it and realized time was up so I quickly coded the solution and debugged it, but didn't explain myself probably because I knew the time was up. Ultimately got both questions right with a minor stumble and then was not asked for a further interview, so I really have no idea why, and unfortunately I understand for legal ramifications why they can't tell me. However not getting past the screen was unexpected.