If you tell your web browser to "remember me" but then delete your cookies, Instagram forgets your device. The next time you try to log in, it will request the 6-digit code.
A 6-digit code for Instagram is a temporary, one-time security number used to verify your identity. It is primarily used for to prevent unauthorized logins, even if someone knows your password. Where to Find Your 6-Digit Code 6 digit code for instagram