If you are using two or more timing systems on the track then you need to make sure you only have one system in the setup screen at one point in time. Also, make sure you do not have your hub firmware 1.20 as this will cause issues. If two or more systems are in the setup screen at the same time then these systems will be seeing and talking to other systems at the same time...which will cause issues.
So you can either make sure you only have one system set up and talking to their respective wireless hardware units at one point in time. Once that first system is in Race mode then you can turn on your next timing station and repeat the process.
Otherwise, if you use the "Use Preconfigured List" option found in Setting General then you can lock the gate/s and start device/s to a single laptop.
Follow these steps to pair your devices to your laptop...Note you will only be able to use these gates/start devices with that laptop, so make them to make sure they all stay together.