There are a few 4D Server settings that can be tested to see whether any of the settings can alleviate the issue.

Toggling network layer
This setting can be found under Database Settings > Compatibility. If you are on the new network layer, try switching to the legacy network layer by checking the box. Likewise if you are on the legacy network layer, uncheck the box and see whether disconnects still occur.

Increase/Decrease client server timeout
Disconnects may occur if a client is temporarily unresponsive longer than the timeout setting. If so, try increasing the timeout and see whether the client continues to be disconnected.

Test connection on blank/new database
This narrow whether the issue is network or environment related, try testing on a brand new database. If the disconnect still occurs on the new database with all default settings, the issue is most likely a network issue based on a VPN/router setting. Otherwise, the issue is environment based in which diagnostic, debug, and wireshark logs should be provided.