I bought these in November 2018 and they were working fine until mid january when the bluetooth started suddenly disconnecting for no reason. This began about 20 minutes into listening and would reconnect after about 15-20 seconds then drop again after less than 10 minutes. After three or four times it didn't reconnect so I checked the player, Astell&kern AK70, and it showed that it was still connected. Trying to disconnect didn't work and just hung the player meaning a reboot was necessary. On restarting I was able to reconnect and had another 20 minutes of music before a disconnection again. This time when the automatic reconnect failed i just switched off bluetooth on the player and restarted and reconnected to the xm3s that way. But, there have been times when it has been necessary to switch the headphones off and on to get a connection.

Note, the player is never more than 2 feet away from the headphones when this is happening, the power can be full or low and it makes no difference. 

In order to rule out a problem with the player I have used it with my Bose QC35s (V1) and a pair of JBL in-ears with no issues. I haven't as yet tried the XM3s with another device though.

I had been looking for a solution and possible firmware update but reading the issues with the latest one I have my doubts.

In relation to the threads about the reduction in the efficiency of the noise "cancelling" - this should be noise reduction, not cancelling - whilst it was good to begin with the quality has degraded over the time i have used the headphones. I can hear conversations when no music is playing or during quiet passages, train announcements are intrusive and airline announcements can be heard over music unless i go to ear damaging volumes. I had expected this problem of degradation to have been addressed as i had the same issue with Sony headphones about 10 years ago, less than six months into using them the noise reduction started to decline to a point where it was non-existent (became a moot point as the headband broke and they went in the bin)

Seems that the XM3s aren't the 5 star product that they first appear to be