First try clearing the browser cache in Internet Explorer:
Note
Although you may have other browsers installed on your computer, Outlook desktop always uses Internet Explorer when rendering web content such as inside Dynamics 365 App for Outlook.
- Clear the cache in Internet Explorer.
https://support.microsoft.com/help/17438/windows-internet-explorer-view-delete-browsing-history
- Close all Internet Explorer and Outlook Desktop windows and make sure through Task Manager there are no remaining Internet Explorer or Outlook processes running.
If this issue only appears in Outlook desktop and clearing the cache via Internet Options does not help, try clearing it via F12 chooser (not applicable for Windows 7):
- Open Dynamics app in Outlook desktop
- Open IEChooser.exe in %WindowsFolder%\System32\F12 (example: C:\Windows\System32\F12)
- Click Dynamics 365
- Click the Network tab and then click the Clear cache button.
After following the steps above, reopen Outlook and the Dynamics 365 App for Outlook to see if the issue is resolved.