Running "dropbox start" with or without "-i" start the daemon (installed in advance - when using "-i" when the daemon is missing). Second launching should be avoided! Even though it shouldn't be a problem, seems Dropbox startup is unstable and has lot of complaints. Algorithm enforcing the work as a singleton application has lot of errors, unfortunately. Does your second try launch detect that the application already runs or not? 🧐 Just bugs! 🤷
I noticed something else. You are running (or trying at least) your application in root content. Running a buggy application (like Dropbox) in expanded permissions could be dangerous for the entire system! Better run such applications in regular user context. Create such if needed.