Ubuntu – pavucontrol stuck at “Establishing connection to PulseAudio. Please wait…”

I sometimes have the problem that I can't hear any sound on my Dell XPS13 with Ubuntu 16.04. I have a Logitech G930 connected to it. When I open pavucontrol it is stuck at "Establishing connection to PulseAudio. Please wait…"
I have been following the Ubuntu Audio Problems Guide (german version is here: https://wiki.ubuntuusers.de/Sound_Problembehebung/#Soundsystem ) and found the following:

$ cat /proc/asound/cards
0 [PCH            ]: HDA-Intel - HDA Intel PCH
                     HDA Intel PCH at 0xdc428000 irq 295
1 [H              ]: USB-Audio - Logitech G933 Gaming Wireless H
                     Logitech Logitech G933 Gaming Wireless H at usb->0000:00:14.0-1, full speed

So the sound cards are recognized.
However, audio is not played:

$ aplay /usr/share/sounds/alsa/Front_Center.wav 
ALSA lib pulse.c:243:(pulse_connect) PulseAudio: Unable to connect: Access denied
aplay: main:722: audio open error: Connection refused

Same with sudo:

$ sudo aplay /usr/share/sounds/alsa/Front_Center.wav
Home directory not accessible: Permission denied
Home directory not accessible: Permission denied
Playing WAVE '/usr/share/sounds/alsa/Front_Center.wav' : Signed 16 bit >Little Endian, Rate 48000 Hz, Mono

The "groups" command does NOT show the audio group, but what I think is strange that it works most of the time (and often so after restarting, if there are problems) so I'd guess it's not the problem.

Where else could I look?

Edit:

$ lspci -nnk | grep -A2 Audio
00:1f.3 Audio device [0403]: Intel Corporation Device [8086:9d71]     (rev 
21)
Subsystem: Dell Device [1028:075b]
Kernel driver in use: snd_hda_intel



$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: ALC3246 Analog [ALC3246 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 7: HDMI 1 [HDMI 1]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 8: HDMI 2 [HDMI 2]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: H [Logitech G933 Gaming Wireless H], device 0: USB Audio     [USB >Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0


$ pactl list short sinks
Connection failure: Access denied