I have the same problem.
I am using OSMC on RPi with HiFBerry Digi board in order to pass-through the audio by SPDIF-Out to my Receiver. Everything has worked great for years, until this last update. Now there is no multichannel sound in SPDIF-out.
Exploring the sound settings in OSMC I discovered that pass-through is now directed to HDMI instead of HifiBerry/SPDIF. Also, my TV is alerting that it detects incompatible sound in HDMI. Unfortunately, the “pass-through output device: HDMI” option is disabled and cannot be changed:-(
Resetting advised by wbeard52 doesn’t work for me.
My log: https://paste.osmc.tv/ebejijowoy
Thanks for any advice!