Help with sensors

I have a garmin speed and cadence sensor which took many attempts to get to work. I am using my iPhone. Used it once just on a ride. It was finally working, so I subscribed. Joined a race and tested before on a ride and worked, so I canceled ride. Joined the race and no longer worked. The speed and cadence sensor say connected but says connection failed on ride screen. When I open the garmin connect ap it says sync failed file transfer error. Please help, ready to give up.