If you find that your speed is not realistic or you are not getting resistance changes, it may be that your smart trainer is not connecting via the correct channel. You can rectify this by turning on the "separate power meter support" option in Advanced Trainer Settings, then connecting your trainer as both the trainer control source AND power source when pairing next time.
First, open FulGaz and un-pair your devices from the connections screen, then continue to the main ride menu. Go into settings (click the "cog" icon in the top right), then scroll down and select Advanced Trainer Settings.
Check the tick-box next to Separate Power Meter Support.
Exit settings, shut down and re-start FulGaz. From now on, you should be given new pairing options when you open the app.
Pair your smart trainer as both trainer control AND power.