Long story short, the solution was to install the latest firmware. In this case, I have an Intel NUC8i7HVK Mini PC with Intel Wireless-AC 8265 and Bluetooth 4.2. I installed the Intel wireless firmware package from experimental:
apt -t experimental install firmware-iwlwifi
This is also running current experimental kernel:
# uname -a Linux nuc8i7hvk01 4.18.0-rc4-amd64 #1 SMP Debian 4.18~rc4-1~exp1 (2018-07-12) x86_64 GNU/Linux
Which provided a more recent load on boot:
[ 2.478527] iwlwifi 0000:06:00.0: firmware: direct-loading firmware iwlwifi-8265-36.ucode
Upon reboot, it was easy to scan, connect, and pair the Logitech MX Anywhere 2S mouse.
For future reference, here are some commands to see some activiites:
$ hcitool dev
Devices:
hci0 0C:54:15:66:3B:9E
$ hciconfig
hci0: Type: Primary Bus: USB
BD Address: 0C:54:15:66:3B:9E ACL MTU: 1021:4 SCO MTU: 96:6
UP RUNNING PSCAN ISCAN
RX bytes:41366 acl:2102 sco:0 events:164 errors:0
TX bytes:4913 acl:29 sco:0 commands:75 errors:0
# bluetoothctl Agent registered [MX Anywhere 2S]# help Menu main: Available commands: ------------------- advertise Advertise Options Submenu scan Scan Options Submenu gatt Generic Attribute Submenu list List available controllers show [ctrl] Controller information selectSelect default controller devices List available devices paired-devices List paired devices system-alias Set controller alias reset-alias Reset controller alias power Set controller power pairable Set controller pairable mode discoverable Set controller discoverable mode agent Enable/disable agent with given capability default-agent Set agent as the default one advertise Enable/disable advertising with given type set-alias Set device alias scan Scan for devices info [dev] Device information pair [dev] Pair with device trust [dev] Trust device untrust [dev] Untrust device block [dev] Block device unblock [dev] Unblock device remove Remove device connect Connect device disconnect [dev] Disconnect device menu Select submenu version Display version quit Quit program exit Quit program help Display help about this program
[MX Anywhere 2S]# paired-devices Device E1:38:CB:49:A9:A5 MX Anywhere 2S [MX Anywhere 2S]# devices Device E1:38:CB:49:A9:A5 MX Anywhere 2S [MX Anywhere 2S]# paired-devices Device E1:38:CB:49:A9:A5 MX Anywhere 2S
Debian wiki on bluetooth: Using Bluetooth in a Debian system
