Currently FusionAuth does not provide additional logging or events for a failed 2FA login.
There are two reasons that a 2FA code would be considered invalid (assuming the code was valid at one point in time):
Expiration. You can control the duration of these codes in the Advanced tab of the edit tenant page by adjusting the external identifier duration for Two-Factor login Another code requested. A user is only allowed one active 2FA code at a time, so if there is a situation where another 2FA code is requested, the other code would be invalidated.It'd be good to see if you can narrow down the situation where the invalid code method is received to one of those, which may help troubleshoot the root cause.