When the phone is connected over bluetooth on Rpi3, it is not possible to synchronize the contacts. 

The dmesg shows massive logs:

 "Bluetooth: hci0: Frame reassembly failed (-84)"

That is known issue with flow control on Rpi3 https://github.com/raspberrypi/firmware/issues/1150.

After /usr/bin/btuart bitrate modification(921600 -> 230400) the contacts are synchronized.

But even with this setup of btuart the log Frame reassembly failed is observed from time to time and contacts sync is hanging.
If the speed 115200 is set, the behavior is more stable.