Does the server share the internet, when connected directly to any other device?
TSW100 is an unmanaged switch, basically a plug and play device, which does the basic switch operation - performs ethernet frame forwarding between your LAN devices. There really is not much you can do in regards to the switch configuration. Besides, since TSW100 operates in Layer 2, it is not aware about internet or any IP related information.
It is not designed to work specifically with Teltonika devices and considering that the switch works, when connected to theRUT240, the issue might be in the server configuration.