B50 dual Bluetooth audio drift

I notice that the audio timing gradually drifts apart when transmitting in SBC to 2 Bluetooth devices. It starts out synchronized and then gradually drifts apart. It takes around 20 minutes before an audible echo is heard between the channels. Reinitialization of Bluetooth transmission resets the timing, but the drift occurs again as before.

Is this typical behavior? Is there a way to keep the timing of both Bluetooth transmission channels synchronized?