Lost-Carrier on WiFi

Hello again, I was wondering if someone knows of a remedy for our customers being dropped after 10-15 minutes, for what appears to be an inactivity/idle-timeout, but shows up in our rad accounting as lost-carrier. If a user stays active, they are not dropped, but if they stop to read a website or walk away for 10-15 minutes, they are dropped. We are not employing the idle-timeout attrib, so I am not sure what is going on. Is this something the radius server is doing, or would the command be coming from our WiFi controller? Thanks in advance for your help!