If an user (eg. user A) has created some custom reports using the "Report builder", the owner id is stored in the field "usercreated" and "usermodified" in the table "mdl_reportbuilder_report".
When merging accounts, from user A to user B, the ownership ID is not being transfered in the table "mdl_reportbuilder_report" to the user B, so the user B can't see the previous reports created by user A.
If an user (eg. user A) has created some custom reports using the "Report builder", the owner id is stored in the field "usercreated" and "usermodified" in the table "mdl_reportbuilder_report". When merging accounts, from user A to user B, the ownership ID is not being transfered in the table "mdl_reportbuilder_report" to the user B, so the user B can't see the previous reports created by user A.