[Steps]
1. Connect speaker to LineOut of Porter
2. Exectute following command
paplay /usr/share/sounds/alsa/Front_Right.wav
Or
aplay /usr/share/sounds/alsa/Front_Right.wav (default sound card is PulseAudio)
3. PulseAudio went to infinite loop and was killed/restarted by systemd automatically. Below log was displayed.
Connection failure: Connection terminated
Stream error: Connection terminated
4. Immediately aplay/paplay again.
5. Playback successfully done without crash.

[Observation]
When sink is in SUSPENDED from PulseAudio point of view it seems to try to resume device and fails, retry, again and again.
This causes infinite loop in PulseAudio.
After its restarting, sink becomes IDLE and change to SUSPEND within approx. 5 sec.
During IDLE state, PulseAudio can successfully start playback to LineOut.

As another observation, this issue has never happen with BB based kernel. And also it has never been observed without PulseAudio like direct access to ALSA device.

aplay -Dplughw:0 /usr/share/sounds/alsa/Front_Right.wav

Therefore this issue seems to be occurred by combination with PulseAudio and ASoC driver.
I had doubt that this issue was caused by the update of ASoC driver.

[Hint?]
Quite similar issue was reported in Debian community.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=828190

[Workaround]
Using USB DAC by changing kernel config (due to Default OFF in renesas kernel), and assign this sink to default-sink of PulseAudio.

1. Change Kernel Config
CONFIG_SND_USB=y
CONFIG_SND_USB_AUDIO=y
2. Connect USD-DAC
3. Check sound card is detected by PulseAudio
pactl list sinks
4. Assign detected sink to default
pactl set-default-sink <sink name>
5. paplay/aplay