XFCE – Fix Xscreensaver Waking Up and Prompting for Password

If you only experience this problem when using VLC see this question

When the screen is blocked, the xscreensaver (version 5.35) password prompt pops out without any mouse/touchpad movement. It just appears, blinks out when the time is gone (there is also a message like "the PAM timeout is cancelled") and appears again. Then the cycle is repeated.

I tried to reinstall it which was not helpful. I'm using Arch (4.7.6-1-ARCH) on a laptop.

Here are the log messages (I removed xscreensaver: in the beginning of all lines). The event I did not trigger is ClientMessage at 10:48:47:

10:48:29: 0: grabbing keyboard on 0xd4... AlreadyGrabbed.
10:48:30: 0: grabbing keyboard on 0xd4... GrabSuccess.
10:48:30: 0: grabbing mouse on 0xd4... GrabSuccess.
10:48:47: DEACTIVATE ClientMessage received.
10:48:47: user is active (ClientMessage)
10:48:47: pam_start ("xscreensaver", "xenohunter", ...) ==> 0 (Success)
10:48:47:   pam_set_item (p, PAM_TTY, ":0.0") ==> 0 (Success)
10:48:47:   pam_authenticate (...) ...
10:48:47:     pam_conversation (ECHO_OFF="Password: ") ...
10:48:47: 0: mouse is at 1047,514.
10:48:47: 0: creating password dialog ("")
10:48:47: grabbing server...
10:48:47: 0: ungrabbing mouse (was 0xd4).
10:48:47: 0: grabbing mouse on 0x140003c... GrabSuccess.
10:48:47: ungrabbing server.
10:49:17: input timed out.
10:49:17:     pam_conversation (...) ==> PAM_CONV_ERR
10:49:17:   pam_authenticate (...) ==> 20 (Authentication token manipulation error)
10:49:17: pam_end (...) ==> 0 (Success)
10:49:17: authentication via PAM timed out.
10:49:17: grabbing server...
10:49:17: 0: ungrabbing mouse (was 0x140003c).
10:49:17: 0: grabbing mouse on 0xd4... GrabSuccess.
10:49:17: ungrabbing server.
10:49:17: 0: moving mouse back to 1047,514.
10:49:17: discarding MotionNotify event.
10:49:17: 0: destroying password dialog.

UPD 2016-10-11

I printed journalctl -p 3 -xb and got tons of such lines:

Oct 08 14:02:57 regulus xscreensaver[12913]: pam_unix(xscreensaver:auth): conversation failed
Oct 08 14:02:57 regulus xscreensaver[12913]: pam_unix(xscreensaver:auth): auth could not identify password for [xenohunter]
Oct 08 14:03:37 regulus xscreensaver[12913]: pam_unix(xscreensaver:auth): conversation failed
Oct 08 14:03:37 regulus xscreensaver[12913]: pam_unix(xscreensaver:auth): auth could not identify password for [xenohunter]
Oct 08 14:04:17 regulus xscreensaver[12913]: pam_unix(xscreensaver:auth): conversation failed
Oct 08 14:04:17 regulus xscreensaver[12913]: pam_unix(xscreensaver:auth): auth could not identify password for [xenohunter]
Oct 08 14:04:57 regulus xscreensaver[12913]: pam_unix(xscreensaver:auth): conversation failed
Oct 08 14:04:57 regulus xscreensaver[12913]: pam_unix(xscreensaver:auth): auth could not identify password for [xenohunter]

The cycle is always 40 seconds which is likely to be the time the password prompt reappears.

I did evtest /dev/input/event${X} where ${X} is every id from xinput list. Plus, I did the same for event streams with id=0 and id=1 which are physical mouse and keyboard. All those streams are empty when the password prompt appears.