I also have this issue.
It turns out that many other people in the support forums have also reported the issue:viewtopic.php?f=12&t=252695&p=843455&hilit=sparkasse#p843455viewtopic.php?f=13&t=226015&p=760215&hilit=sparkasse#p760215viewtopic.php?f=13&t=36879&hilit=sparkasse&start=10
Apparently the issue is that the first stage, where the user is required to enter the username first (similar to how gmail requires the username, then a separate window/step appears to enter the password) is 'dynamically' named, which seems to confuse LassPass somehow (see the third link above for more details). There was someone from LassPass looking into it, but it seems they have not responded to all of the users reporting this issue. The fixes that other users suggested that LassPass' engineers could look into were:
1. Exploiting the fact that when we navigate to:https://login.sparkasse.at/sts/oauth/au ... orgeclient
the username field is selected by default, i.e. Lastpass could see the above URL and just autofill the username, let the user click the 'start login' button, then autofill the password as well (similar to how we log in to gmail).
2. Exploiting the fact that the field does have a 'User number' or 'Verfügernummer' label (depending if the user is using the website in English or German), to find and fill the field.
Would really appreciate an update from LastPass given how long it has been an issue now (many years).