By default, Safari browser security settings blocks Website tracking: Prevent cross-site tracking, which prevents Noteflight worksheets from opening.
Users will see this screen when attempting to open a Worksheet from Safari:
To resolve, from the Safari browser, click Safari (top left corner), select Preferences, click on Privacy, and remove the checkmark from Prevent cross-site tracking as shown below:
Retry opening the Worksheet. The Worksheet should now open correctly.