Today my BT lost connection 5 times during 4 hours. Reconnected only after turn off/on BT on phone.
Switch to 6.1.21 didn't fix problem.
Try any other FW?
Try tomorrow without MiBand?
Sell MiBand and use one BT device? :)
I almost don't have problem with MiBand (I have 1S model). Only with jabra headset.
Already downloaded to phone 6.1.21 firmware. Tomorrow will be the first results.