Hi
In the latest firmware, there are new settings to adjust timeout/retries in the radius-server config under "User-Accounts" as in screenshot attached. That should allow you to increase the timeouts (and maybe retries too) so as to allow the duo-service to complete the auth-process and send back the confirmation to RV34X
The version iam using is v1.0.03.21 on RV345
hope this helps