Many people prefer using an OTG cable to connect the Spark remote to their tablet/phone. The theory being that a cable is more reliable than a WiFi connection. DJI did not design the Spark remote to be connected in this fashion but it does seem to work, depending on firmware and version of DJI Go.
Personally I have never had any issues using just WiFi between my tablet and remote. They are literally 2 inches away from each other and it's very stable for me.