GW 18.1.1 eDir authentication ignored

Hello together,

we have upgraded from GW 14.2.3 to GW 18.1.1 and now have troubles with authentication.
LDAP was configured before with Single SignOn enabled on the Postoffices and it worked.
The settings show up up as active after the upgrade, but the users are prompted to enter the eDir password when launching the GroupWise-Client.
Already disabled and re-enabled the setting on PO, but no effect.
The only way to get it working is to go to the user object and disable Network Authentication / Single SignOn, save settings, wait one to three seconds and re-enable.
Is there any way to solve this other than open each user account (1.000 accounts) ?
Any help appreciated.