Atheros bluetooth receiver drops out periodically, Dell Inspiron 15

I have a fairly old Dell Inspiron that I'm using temporarily, running Ubuntu 21.10. Every once in a while, maybe once every couple of hours, the Bluetooth software in the laptop fails. By that, I mean that the Bluetooth icon on the xfce menu toolbar disappears, the mouse stops working, and I get an alert on the screen saying that the mouse has disconnected. Generally about a minute later, the software comes back and the mouse reconnects.

I am pretty sure this has nothing to do with the mouse, because I've tried another mouse and have experienced the exact same behavior. On one occasion, the Bluetooth device/software on the laptop completely stopped working, and I had to power cycle the laptop to bring it back.

I think the Atheros hardware also powers the laptop wifi, and I have had no problems whatsoever with that. However, from looking around on the web, it seems that the Dell implementation with those Qualcomm Atheros chips is just sub-par and fails a lot; there may be nothing I can do about it. Any suggestions are welcome.

e: I note in the kernel log that when it fails, I get:

Bluetooth: hci0: setting interface failed (110)

logged. Apparently the device is on the USB bus internally, so it shuts down and then the kernel recognizes it as a new USB device when it regains consciousness. Also it's somewhat weird and amusing that the device (the Atheros chip) identifies itself as "Alaska Day 2006".

edit — in response to a comment, here's some more information on the machine:

iw dev

iw dev
phy#0
    Interface wlp2s0
        ifindex 3
        wdev 0x1
        addr 9c:2a:70:51:b1:d5
        type managed
        txpower 15.00 dBm
        multicast TXQ:
            qsz-byt qsz-pkt flows   drops   marks   overlmt hashcol tx-bytes    tx-packets
            0   0   0   0   0   0   0   0       0

ifconfig -a

enp1s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.50.126  netmask 255.255.255.0  broadcast 192.168.50.255
        inet6 fe80::a584:4321:e579:c9bc  prefixlen 64  scopeid 0x20<link>
        ether b8:ca:3a:dc:ec:85  txqueuelen 1000  (Ethernet)
        RX packets 9811652  bytes 11389507665 (11.3 GB)
        RX errors 0  dropped 293  overruns 0  frame 0
        TX packets 6309872  bytes 1786202302 (1.7 GB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 10782  bytes 1095652 (1.0 MB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 10782  bytes 1095652 (1.0 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlp2s0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether 9c:2a:70:51:b1:d5  txqueuelen 1000  (Ethernet)
        RX packets 9096676  bytes 11343332985 (11.3 GB)
        RX errors 0  dropped 314441  overruns 0  frame 0
        TX packets 3177922  bytes 416764411 (416.7 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

(running on wired Ethernet at the time that was captured)

inxi -F

System:    Host: deltron Kernel: 5.13.0-30-generic x86_64 bits: 64 Desktop: Xfce 4.16.0 Distro: Ubuntu 21.10 (Impish Indri) 
Machine:   Type: Portable System: Dell product: Inspiron 3521 v: A04 serial: 1T20GW1 
           Mobo: Dell model: 0010T1 v: A00 serial: .1T20GW1.CN1296631P0BC4. UEFI-[Legacy]: Dell v: A04 date: 11/21/2012 
Battery:   ID-1: BAT1 charge: 57.0 Wh (100.0%) condition: 57.0/65.5 Wh (87.0%) 
CPU:       Info: Dual Core model: Intel Core i5-3337U bits: 64 type: MT MCP cache: L2: 3 MiB 
           Speed: 1796 MHz min/max: 800/2700 MHz Core speeds (MHz): 1: 1796 2: 219 3: 327 4: 576 
Graphics:  Device-1: Intel 3rd Gen Core processor Graphics driver: i915 v: kernel 
           Device-2: Realtek Integrated Webcam HD type: USB driver: uvcvideo 
           Device-3: Elgato Systems Cam Link 4K type: USB driver: hid-generic,snd-usb-audio,usbhid,uvcvideo 
           Display: server: X.Org 1.20.13 driver: loaded: modesetting unloaded: fbdev,vesa resolution: 1: 1366x768~60Hz 
           2: 1920x1080~60Hz 
           OpenGL: renderer: Mesa DRI Intel HD Graphics 4000 (IVB GT2) v: 4.2 Mesa 21.2.6 
Audio:     Device-1: Intel 7 Series/C216 Family High Definition Audio driver: snd_hda_intel 
           Device-2: Elgato Systems Cam Link 4K type: USB driver: hid-generic,snd-usb-audio,usbhid,uvcvideo 
           Sound Server-1: ALSA v: k5.13.0-30-generic running: yes 
           Sound Server-2: PulseAudio v: 15.0 running: yes 
           Sound Server-3: PipeWire v: 0.3.32 running: yes 
Network:   Device-1: Realtek RTL810xE PCI Express Fast Ethernet driver: r8169 
           IF: enp1s0 state: up speed: 100 Mbps duplex: full mac: b8:ca:3a:dc:ec:85 
           Device-2: Qualcomm Atheros AR9485 Wireless Network Adapter driver: ath9k 
           IF: wlp2s0 state: down mac: 9c:2a:70:51:b1:d5 
Bluetooth: Device-1: Qualcomm Atheros Bluetooth USB Host Controller type: USB driver: btusb 
           Report: hciconfig ID: hci0 state: up address: 9C:2A:70:51:B1:D6 bt-v: 2.1 
Drives:    Local Storage: total: 2.4 TiB used: 899.62 GiB (36.6%) 
           ID-1: /dev/sda vendor: Western Digital model: WD6400BPVT-22HXZT1 size: 596.17 GiB 
           ID-2: /dev/sdb type: USB vendor: Western Digital model: WD My Book 25DA size: 1.82 TiB 
Partition: ID-1: / size: 585.25 GiB used: 14.33 GiB (2.4%) fs: ext4 dev: /dev/sda3 
           ID-2: /boot/efi size: 512 MiB used: 5.2 MiB (1.0%) fs: vfat dev: /dev/sda2 
Swap:      ID-1: swap-1 type: file size: 2 GiB used: 0 KiB (0.0%) file: /swapfile 
Sensors:   System Temperatures: cpu: 47.0 C mobo: N/A 
           Fan Speeds (RPM): cpu: 2600 
Info:      Processes: 253 Uptime: 7d 2h 6m Memory: 15.51 GiB used: 7.07 GiB (45.6%) Shell: Zsh inxi: 3.3.06 

EDIT:

It appears you have a Qualcomm Atheros AR9485 wifi adapter, which is not integrated with BT.

Related:

1. Qualcomm Atheros AR9485 Wireless Network Adapter not working on Ubuntu 13.10
2. http://linux-hardware.org/?id=pci:168c-0032-103c-1785

"Any suggestions are welcome". Here you are:

1. Try identifying whether bluetooth and wifi may be interfering with each other. For instance, disable wifi for a while (if you can work with cable internet, or nothing at all), enough to have some confidence (even if not certain) on the result. To achieve this, there are several options, e.g., nmcli networking off. See also How to disable wireless from command line, https://www.ubuntupit.com/how-to-disable-wifi-on-linux-system-gui-and-cli-methods/. The usual case is that for integrated WiFi+BT cards, if there are issues it is WiFi which is most affected. E.g. Errors in make defconfig-ath10k .. Slow wifi with qualcomm Atheros QCA9377, Why is my WiFi connection erratic after upgrading to 21.10?. Opposite what you are seeing, if this interference is the culprit.

2. Please post the complete PC model. And further info from commands below (depending on what you post, additional info may be requested). It is essential to know the hardware and drivers you have.

   $ iw dev
   $ ifconfig -a
   $ inxi -F
   $ dmesg | grep ath
   $ lspci -knn | grep Net -A3
   $ lsmod
   

3. Without further information, solutions posted here may be worth trying. Something like broad spectrum antibiotics, until we know more.

Someone else with a computer from 2013 had the same problem with Ubuntu 20.10 derivative called Pop OS 20.10:

• [Solved] Bluetooth down and hciconfig hci0 up timeout

You should definitely read the entire thread on Arch Linux forum but the solution is to use:

hciconfig hci0 down
rmmod btusb
modprobe btusb
hciconfig hci0 up

The other doesn't state it but you should use sudo first.