It had seemed abandoned for a while, but I remember reading that Vessel had an update a few weeks (or more) ago. You might make sure that you have the latest version. I haven't used it recently, though, and I've never used it on mac, so I don't know if the freezing is normal or not.

If, by "can't sign in", you are talking about how vessel opens when steemconnect prompts you to open the desktop app from your browser, I am not sure if that will work. You'd probably need to download the steemconnect desktop app, or just "import keys" in your browser. They've been making a lot of steemconnect changes recently, and it's not always very intuitive...