radius-proxy: reason-code 117: The remote RADIUS (Remote Authentication Dial-In User Service) server did not respond

we quite frequently log those events on our main radius-proxy:
---
Access request for user hansi was discarded.
...
NAS-Identifier = <not present>
Called-Station-Identifier = <not present>
Calling-Station-Identifier = <not present>
...
NAS-Port-Type = Virtual
...
Proxy-Policy-Name = policyxyz
Authentication-Provider = RADIUS Proxy
...
Reason-Code = 117
Reason = The remote RADIUS (Remote Authentication Dial-In User Service) server did not respond.
---
---
which a second later is followed by:

User hansi was denied access.
Fully-Qualified-User-Name = <undetermined>
...
NAS-Identifier = <not present>
Called-Station-Identifier = <not present>
Calling-Station-Identifier = <not present>
...
NAS-Port-Type = Virtual
...
Proxy-Policy-Name = hansi - hansi mueller
Authentication-Provider = RADIUS Proxy
...
Policy-Name = <undetermined>
Authentication-Type = <undetermined>
EAP-Type = <undetermined>
Reason-Code = 112
Reason = The remote RADIUS (Remote Authentication Dial-In User Service) server did not process the authentication request
---

>> our "timeout" in the remote-connection policy is 7 seconds (which should suffice i reckon). furthermore there is an entry for a second server with priority=2 as a fallback, which is not tried to contact even in this case (but does work nevertheless in case the first server is unavail.


i could not find any resources speaking of "reason-code = 117" - any suggestions?