I have an external team ("Community Villa" below) unable to access the issue type they are supposed to be able to see:

Basically, Community Villa is supposed to have access only to a certain type of issues (called "Content idea").
I've set the security scheme by putting our employee group as default Security Level field, so every task that has that field automatically prevents Community Villa from entering.
However, Content idea issue types don't have the Security Level field:

Project permission for their group to browse the project is active. Therefore, the alert makes no sense to me, seems more like a bug (especially because they seem to be able to access other tasks of the same type).