SteelSeries Arctis 5 (2019) edition has a new device ID
The SteelSeries Arctis 5 (2019) edition has a new USB ID. So, PulseAudio isn't picking up the special dual channel configuration for the chat (mono) and stereo channels.
lsusb output
Bus 001 Device 013: ID 1038:12aa SteelSeries ApS
I made the following addition in /lib/udev/rules.d/90-pulseaudio.rules
:
ATTRS{idVendor}=="1038", ATTRS{idProduct}=="12aa", ENV{PULSE_PROFILE_SET}="steelseries-arctis-5-usb-audio.conf"