UI Theme has changed back to UI16 from Next ExperienceIssue System UI reverted to UI16 even though the instance supports Next Experience UI and settings are there to show Next Experience UI.ReleaseSan Diego and aboveCauseThe issue could happen due to adding/ modifying the below user preference: Name: glide.ui.polaris.use URL: https://<Instance_name>.service-now.com/sys_user_preference_list.do?sysparm_query=nameLIKEpolaris.use&sysparm_view=Value: FalseNotice that this user preference is set as a system preference, this means the preference would apply to all users who do not have glide.ui.polaris.use explicitly set to true.ResolutionTo resolve the issue, please make sure that the glide.ui.polaris.use system user preference is set to True.