Change your system date to 27-03-2022 (UTC +01:00 Amsterdam, Berlin, Bern, Rome, Stockholm, Vienna) and make sure you enable "Adjust for daylight saving time automatically".
This is the day that daylight saving adds one hour.
Go to https://syncfusion-scheduler-horizontal-scrollbar-latestversion.stackblitz.io/
As you probably see now, is that all dates are shown twice:
On other days of the year, this is not the case.
This is a TimelineWeek schedule, I noticed that the same happens in the TimelineDay schedule.
It probably has something to do with the combination of the TimelineWeek/TimelineDay schedule in combination with the Timescale Customization.
You can see/edit the code of the Stackblitz here: https://stackblitz.com/edit/syncfusion-scheduler-horizontal-scrollbar-latestversion?file=app.component.ts
Can you please investigate this issue? Thanks in advance.