RADIUS Timeout >> Cannot assign requested address

Hi …
i do have a running setup with a CRS doing dynamic VLANs for copper interfaces and Wireless with the support of CAPSMAN/USERMANAGER and RADIUS/DOT1x authentication for the ethernet ports.
Now i wanted to extend that setup and put some switches “underneath” offering just the copper part via DOT1x.
I can successfully connect the switches and use them through the standard VLAN-Setup, but not via RADIUS and DOT1x.
Switches are also connected through management VLAN which also has the Radius-Server in - general connectivity works / f.e. update check works as designed
For RADIUS I always get timeouts on those connected switches if it comes to the RADIUS communication.
within the Log i can see the following message >>


The target CRS has an entry for the Switch IP within the Router-Section of UserManager - external Queries to the UserManager from other Ethernet-Ports work, checked it with NTRadPing.
error02.png
any idea what i am missing …
error01.png