If Auto Scroll is enabled, event track can't trigger, so events may not fire. The frame numbers appear to be duplicated. Especially noticeable when the [View Range End Time] is small value (Working Auto Scroll).
Custom events always fire and output log every second.
Some custom event can't trigger.
Reproduced when play sequencer after simulate attached project.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-87587 in the post.