There is a PDF attachment on a custom object, this is opening fine in Classic but in Lightning it throws Insufficient Privileges error (in a classic window) as below when user tries to view it. Note this happens for Admin user.
Insufficient Privileges You do not have the level of access necessary to perform the operation you requested. Please contact the owner of the record or your administrator if access is necessary. For more information, see Insufficient Privileges Errors.
This PDF attachment is created from a managed package, but as far as I can see there is no access issue. Appreciate any help to resolve it. Thanks.