Edge 530 and coros hrm armband

I am trying to use the coros armband with my garmin edge 530 and it keeps disconnecting and connecting every few seconds.

Since I started using it (2 weeks - 5 rides), I only managed to record my HR data on one ride. And now I spend all the ride seeing that the rest of the sensors (speed / cadence, powermeter, telephone...) do the same connect / disconnect thing.

Does anyone know how to solve it?