I heard a lot about that a few months ago, but they've improved their detection algorithm since then. You can try emailing support and ask to be whitelisted, but past that I'm not sure if there's anything you can do. I've never had that problem with them, so I didn't look too closely into the resolution of it back when it was more common. If you do a few searches for "coinbase high risk" you may be able to find something useful however.