A user experiences the following symptoms in Office 365:
Icons are missing from the tiles in the Office 365 app launcher.
In Outlook on the web, the icons in the upper-right area of the page are missing. For example, the Help and Settings icon are missing.
This occurs if the Untrusted Font Blocking feature is enabled on the computer as part of either a domain group policy or a local policy. Office 365 icons are glyphs that are saved in an Office 365-designated font. When the policy setting is enabled, glyphs from the font aren't visible.
Turn off the Untrusted Font Blocking feature. For more information about how to do this, see the following Microsoft Knowledge Base article:
3053676 Windows 10 Technical Preview adds a feature that blocks untrusted fonts