[random2021]

since you told me I am using a I tried without 2FA code but with backup-code

> When I click the second link, I'm forced to reauthenticate.

Here, I am being asked my password.

Then get that page.

[codetrotter]

Probably the difference, like parent says, is that you recently used 2FA, from the same OP address etc etc, so even though you have signed in with backup code now Google still trust your sign in more than OP.