Heart Rate Monitor disconnects, any tips?

I have just finished WTRL TTT race and my HR monitor cut out 30 seconds into the race. I did have a Garmin ant+ but it was always cutting out so now I have a Bluetooth one and it does the same sometimes like today. I reconnected it and it stayed connected for the rest of the race 40 mins. Zwift log does not show any errors. I had my phone on but Bluetooth turned off?