For some reason now it works properly.

NOTE: this solution is unstable and can change in the future.

src/app/(sidebar)/contacts/[contactId]/edit/page.tsx

@@ -9,9 +9,7 @@ async function editContact(contactId: string, formData: FormData) {
   "use server";
   const updates = Object.fromEntries(formData);
   await updateContact(contactId, updates);
-  revalidatePath('/(sidebar)', 'layout');
-  revalidatePath(`/contacts/${contactId}`, 'page');
-  revalidatePath(`/contacts/${contactId}/edit`, 'page');
+  revalidatePath('/(sidebar)', 'layout');  // THE NESTED BEHAVIOR IS UNSTABLE AND CAN CHANGE IN FUTURE.
   redirect(`/contacts/${contactId}`);  // This makes the server component data be reloaded.
   /*
    * The server component architecture is a HTMX-like structure where the component rendered is STATE-LESS