A licensee has encountered a crash when loading Sequencer Assets that occurs in BlendSegment during a sort lambda. It's possible to end up in a situation where the SourceIndex being sorted is larger than the Sections array. We've been able to reproduce this by cutting/splitting a camera anim section.
Either run the automated tests located at System.Engine.Sequencer.Compiler (you'll have to back out 3380551 locally), or make a camera anim track that has multiple overlapping sections on multiple rows.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-43446 in the post.