I'm using OpenVPN radiusplugin, and I found this problem days ago.
Every hour openvpn server will attempt to rekey to client, at this time radiusplugin will made an Accounting-Request to openvpn server.
But I have set up Simultaneous-Use,thus the plugin will get an "already log in" reply message.
So openvpn client will disconnect every hour and ping-restart itself.
The default SQL to check Simultaneous-Use is:
simul_count_query = "SELECT COUNT(*) \ FROM ${acct_table1} \ WHERE username = '%{SQL-User-Name}' \ AND acctstoptime IS NULL"
which definately will cause problem if radiusplugin post Accounting-Request when rekeying.