I've had similar issues -- consider it a bug -- and unpair and re-pair with your phone, and likely the issue will go away.

I think I unpaired it, but I cannot pair it again, as it isn't recognized by the iPhone at all.

i’ve had this happen due to going from beta builds to stable builds or vice versa. not super clear exactly which of those triggered it, or whether it was just a beta build bug, but the 5x reboot always fixes it