Following formula will validate if Assignee user by name os the logged in user.
See report example Issues created vs resolved by priority in our Demo account. The calculated member Support and current assignee in dimension Assignee uses the formula above to retrieve a logged in user by name. The formula for Support and current assignee will work for cases when currently logged in user should see assigned issues and issued assigned to some specific other user. You can select this calculated member on Pages to filter issues a user should work on.
When using eazyBI for Jira, default user dimensions like Logged By, Assignee, Reporter, use CurrentUser function which returns user key as user name and user key do not match for these dimension members.