Hmm, well I never run with "Use secure session keys and login page" unchecked so I'm not fully aware of how that behaves.
But I would expect your tablet there to be given an administrator session automatically because of being a whitelisted address, and even if that function was not working then it should be getting an anonymous session because of being a LAN address.
Lets back up a bit.
What does it look like when you are asked for credentials? Can you screenshot that?
This is just the web browser informing you that you didn't use HTTPS, which is completely normal because
Blue Iris does not support HTTPS natively with its web server.