On the Task Timeline view in the Modern UX, the 'Show Dependencies' checkbox will not remain on. Since the box will not remain checked, the dependencies are not displayed and cannot be added/edited.
What needs to be done to make it to where the 'Show Dependencies' checkbox will remain checked?
Upgrade to Clarity 15.9.3 in order to resolve the issue.
Until then, the workaround is to review the views having the issue and delete and recreate the view.