After upgrade, sometimes it is reported that the Related Records Tab on Case(sn_customerservice_case) Form is not available when there is a Problem is associated with the case record.
From the code level, the roles that are needed to see the related records table is either itil or sn_problem_read, as defined by the below 2 Script Includes:
On top of it, the details of this section are managed by the below Script include:
It could be possible, that the user might have modified the above Script Include
Please check if the user has those roles or not.
If the user does, and if the user has modified the above script include (sys_id=d5acd7d2d7123100b7490ee60e6103f4), try to revert it to OOB.