The entire process was extremely slow on their end. I didn't hear from any recruiters until two months after I gave them my info in person. Not unreasonable, if a bit slow for this industry, but it was a sign of the speed of the rest of the process.
After the phone screen, they asked me for on-site availability, which I sent. The recruiting team then was unresponsive for two weeks. When they got back to me, they told me this was because they were out at a conference during the week I'd given availability for; though that conference was only two days long, so I'm not sure what the hold-up was.
It took another two weeks after the interview for them to send me their decision.
The technical phone screen was pretty typical - an overview of the team, some questions about application security, and questions for the candidate.
The on-site was rather disorganized. The recruiter did not inform me that I would need to bring a laptop for not one, but two coding/code review sessions. Fortunately, I did have one with me in case I needed to kill time between the interview and my train back; but if I'd known, I would've brought a better and more familiar laptop with toolchains installed (the coding exercise was supposed to require Docker/Node, which I didn't have on that laptop) and a fully-charged battery. In addition, there was additional delay because I wasn't given a WiFi code for the captive portal when I signed in. (I did ask for one, but the front desk printed me two badges instead)
During the on-site, I was informed that they were quickly trying to staff security engineers on both the Ecosystems and the internal Product Security teams, though the recruiter only put me in for the former. I'm not really sure why, because that team seemed to be looking for builders/coders - which I made abundantly clear, during both the phone and on-site interviews, is not something I've done in a while. This was probably a primary reason for rejection, though I can't say for sure because I didn't get feedback.
I was supposed to have a company values interview with the Diversity head, but that didn't happen - and given how much emphasis on the values was impressed upon me (including by the hiring manager), it felt like an indication that they were not interested in me as a candidate from the get-go. I instead got to spend extra time with the same person who interviewed me over the phone, and who also covered the beginning of a session for an interviewer who was running a bit late, even though I was only supposed to spend 15 minutes with him during the on-site. Nothing against the guy; I just started running out of questions to ask about the team/role, after having all this time with him.
I should also note that half the interviews were done by videoconference. Not a bad thing, though it did cause issues when I needed something in-person (WiFi issue mentioned previously).
Second session was code review of code samples in different languages, downloaded to view on my own laptop. The interviewer for this session was friendly and did not add any pressure to answer when I was responding slowly, which I appreciated. I could've been faster with a more familiar laptop and if I wasn't as nervous, but this session was extremely fair and not very difficult.
Third session was called "Technical & Team Fit" in the schedule. The schedule made no mention of a CoderPad session, which as mentioned above did not go smoothly because of the laptop I did(n't) bring. The interviewer spent the other half of the time on an extremely broad question (how would you design everything - both technical controls and policies and human coordination - for security in a pipeline) that I had difficulty finding a starting point on, so that did not go well either. The interviewer could've been better about offering leading questions to give the candidate an area to talk about. Interviewer was a bit late, so we didn't get to go over introductions.
Last session was a typical management interview with the CISO, but done in a more natural/conversational style than the typically-rattled-off-list of "Tell me about a time when...". He seemed like a pretty cool person.
The schedule didn't account for any time for bathroom or other breaks, though I of course didn't have any problems requesting this from interviewers. They kept me pretty hydrated, but I was hungry by the end of the interview (which was scheduled to avoid including lunch) - I would've appreciated if someone had offered me a snack (either from the kitchen, or just to make it socially acceptable for me to eat the snack I'd brought from home during the interview). The interview ended right on time. There was not a recruiter to walk me out or do a wrap-up feedback session.
TLDR - Recruiting team needs to work on promptness and logistics.