According to reports from readers, the page for depositing checks in the app currently cannot be opened while in China, and it will show a message saying the feature is unavailable in certain countries. If you switch your VPN to the U.S., the check deposit screen should open normally again. My guess is that BofA is doing this to prevent counterfeit checks, someone else’s checks, or bad checks.
If you’re going back to China, keep this in mind. It’s best to use a U.S. VPN when logging in to various bank apps; otherwise, there’s a good chance you could trigger fraud or risk controls, which can be quite troublesome.