Scheduler - Event disappears if start is not in viewport

It looks like a CSS issue. You can see that there is a small arrow in place of the event. This arrow is part of the floating event div that gets activated for events that start before the viewport start.

Does it happen with the default CSS theme as well?

I am using the default theme, I am just changing colours on the before render events. I have turned floating events off and it works fine for what I need.

Thanks for the update!