I use a setup where I record 27 h 7 d sensor data with a training tracker. I had problems with two identical Garmin watches, two Polar OH1 sensors, and two Polar H7. What is working now is a Galaxy S5 with ANT+, and two Polar OH1 sensors used alternatively, one recording sensor data, one charging. One Polar OH1 is paired over ANT+, the other over BLE.
Peter Gamma