OneSignal Software Engineer interview questions

1) Sourcing call, 2) Coding screen, 3) HM screen, 4) Full loop. 1) Recruiter was 10+ minutes late but one of the most pleasant people I've spoken with. Conversation was energetic and productive. Absolute silence for more than a week afterward. 2) Coding screen was a multi-stage, progressive coding challenge. 3) Hiring manager postponed and rescheduled, thus prolonging the interview process further. Then on camera, they were visibly disinterested and distracted. Despite this, I thought this STAR-format conversation went fairly well. Received a copypasta rejection email days later without explanation and no route to follow-up. What an incredible waste of interviewees' time.