Comment 5 for bug 1859592

I also had this issue, which first manifested by bluetoothd being completely unresponsive and being unkillable, even with SIGKILL. The whole system would lag at regular intervals.

After a hot reboot (no power cycle), the lag went away but it was impossible to activate bluetooth and dmesg showed the same messages as above:

Bluetooth: hci0: command 0xfc05 tx timeout
Bluetooth: hci0: Reading Intel version information failed

Finally after a cold power off and then back on, everything started working again. So it would seem that there is actually some hardware bug here, because the issue persists across reboots if the bluetooth chip is not power cycled.