Case Manager role not able to see case conversations that have been migrated from legacy system

Summary:

My client is going live on Monday with HR Help Desk and Case Management, we are migrating over their current SRs and Cases from their legacy system and have also moved over their Case Conversations and notes, the users have the OOTB Case Manager role but while reconciling the data they are not able to see the case conversations of any cases where the data has been migrated, if the case is new and there is a case conversation they are able to see these ones. I have checked Access Groups and made sure the Conversations object is active which