Salesforce Classic vs. Lightning Experience Issues

These issues are caused by switching between Salesforce Classic and Lightning Experience.
Issue Solution
A UI check incorrectly returns Theme4t instead of Theme3 when the user is using the Classic UI on mobile devices. This issue occurs with Visualforce global $User.UIThemeDisplayed and Apex class UserInfo.getUiThemeDisplayed commands. Check the user’s current UI by verifying if the sforce.one JavaScript object is available; this object is not available in the Classic UI.