That's not a database setting, get the developer to check the app again. SQL won't automatically close connections (I've left connections open for days or weeks)
Only way it can be on the DB side is if there's a job that someone wrote that's killing connections older than a certain age, someone's manually killing connections or the DB or server is restarting on a regular basis.
Also, check the network between client and server, if that has regular drops it could explain the disconnections.
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