Hi @Tommaso2 

Refer: https://www.servicenow.com/community/csm-forum/contextual-sidebar-panel/m-p/2400221

1) repair ui builder plugin and check

2) Can you try this.

• Navigate to System Properties > User Preferences (or sys_user_preference.list).
• Search for workspace.showAgentAssist.
• Set its Value to false and System value to true, then save

check it. 

If not working raise a case to your servicenow vendor. ( hi ticket)