what is your exact OBIEE version?
Did you have a look in MOS? There is a bug and a patch related to catalog and permissions, not sure if it's the same one you are having or not ...
Looks like you are facing this issue because of the users which existed in OBIEE 11g doesn't exist in OBIEE 12c, did you perform steps to migrate users from 11g to 12c.
a) For users in OBIEE 11g Embedded LDAP then you need to manually migrate the users by exporting security data from 11g and then importing the security data in 12c.
b) For users in OBIEE 11g External LDAP(Active Directory, Oracle Internet Directory etc..) then you need to manually configure LDAP provider in your OBIEE 12c instance to get all the users which are present in OBIEE 11g.
Using Alternative Authentication Providers
However same issue is described in below KM document:
OBIEE 11g: After Patchset Upgrade, Changing Permissions On Any New Or Existing Dashboard Fails With Error 'Assertion Failure: !tAccountID.isEmpty()...' (Doc ID 2107371.1)
Since above document is for 11g to perform catalog validation in OBIEE 12c follow below link under section "16.2.4 Validating the Catalog"
Just to be on safer side take your service instance backup using exportserviceinstance command from WLST scripting tool before performing validation steps.
Thanks and Regards,
Syed Hamd Salman
Iam not sure what is MOS but our current version is the following one
Oracle Business Intelligence 220.127.116.11.0
MOS means My Oracle Support