[USR-TC] leased lines by NETServer 16

one of our netservers stops listening for leased line (&l1 is set). it happens after disconnecting of user. port is off (not red/yellow/green). i checked init strings and NVRAM settings - everything is same as on other netservers. reseting port dont help. i wrote &l1 option into nvram and rewrite init string by atz and same problem. any suggestions? (NETServer 16 - OS V3.8.1 modems - V1.0.8)