On Sambung S8 phone, Samsung browser, tried to log in to Dropbox free, basic account using email address & password. Two factor authentication sent me email with 6 digit authentication code. Opened gmail to get code, memorized code, then returned to Samsung browser to enter the code. When I clicked on browser, it cleared current page, returning me to log-in page to re-enter email address & password, as if cache memory had been cleared at app swapping from browser-Gmail-Browser.
I cleared all cache files, background apps, tried to login again, but got the same problem.
With the restarted login, the prior 6 digit code is no longer valid, so I am in a doom loop forever, and can never access dropbox through my phone while 2 Factor Authenication is on.