Performance of login with AA

2FA login with Advanced Authentication is quite a lengthy process. After a user has entered a username it takes 10 to 20 seconds until the selection of the chain.

Are there any ways to optimize this?

My guess is that it has to do with the number of user and/or group objects. While we tested AA with a few users we did not see any slow login performance.

Another idea is that it could be related to the version. Coincidentally at the same time when we changed from a few test accounts to productive operation with about 5000 accounts there was the upgrade to 6.4.2.

Are there any known performance losses with 6.4.2 or 6.4.3?

We have clustered AA 6.4.3 with 2 DB servers, 2 web servers  and NGINX loadbalancer.