"The bliss of ignorance", I don't think we use these words, but I will interpret that as how some people like the feeling of not knowing about Dukkha, ignoring the facts of life and somehow believing that all their good fortune is permanent. Sometimes people will have what we call the "happiness of ignorance," allowing themselves to believe that all the worldly happiness they have will be permanent and everlasting.
"Resting in the not knowing", when I say this, usually in the 5 Hindrances talk, it's about becoming comfortable with not knowing, not trying to form concepts and opinions about life, or ultimate reality, or things that we haven't yet experienced. Instead opening to that feeling of not knowing, which is sometimes very difficult for us, to actually admit that we do not know. This often makes us feel a bit insecure. So, there is a tendency in the mind when we meet those places where we really don't know, and we have to just open to the not knowing, that the ego may wish to rush in and make us feel better by creating some ideas about reality or about what we are experiencing, to make us feel more comfortable. That is usually what I mean by "resting in the not knowing," becoming comfortable with not knowing. It is ok not to know. As long as we start to see that what we are doing is actually decreasing our suffering moment by moment, then we know we are going in the right direction. This can also help us to become more comfortable not knowing what ultimate reality is, or the end of the road, because even if we don't know what it exactly is, we know we are walking in a good direction.