Only happens on iOS when creating a new textbox. Steps to reproduce: 1. Visit <http://portal.office.com> and sign in. 2. Open Visio and create a new document. 3. Click on the Textbox button in the Home toolbar. 4. Drag a selection to create the Textbox. Then the caret appears on Mac, but it does not on iOS. Though you can still type if you have a hardware keyboard attached.
<rdar://problem/48695127>
The content editable or text field or whatever Microsoft is using is not focused on iOS so we do not show the keyboard candidate bar. Typing is allowed because Visio handles events even when there is no focused element.