If the 4D app is still experiencing disconnections issues on both legacy and network layer, try checking for any calls to SET DATABASE PARAMETER(Idle connections timeout;numSeconds). This setting specifically controls the maximum period of inactivity before a client/server session is placed into a "Postponed" state and the network socket is closed. The socket will automatically be reopened upon any new user activity.

While the default is set to 20 seconds, it is recommended to keep this setting between 20 to 60 seconds. However, for troubleshooting purposes, it could be worth trying 0 seconds to never allow 4D to close an idle TCP socket and see whether disconnections still occur.