Same problem here. I have tried many times and cleared cache. Nothing works except when I press bixby button. If I press this button, right after for a few seconds, voice wake up will work. It then stops after this. I hope samsung will respond by fixing this glitch.
@user0OP1YvohEk it does seem strange that you are having difficulty with Bixby and Google Assistant, maybe we can look into the cause of this if you'd like. I'll be happy to assist you if you provide me with your model number, Baseband version, and carrier. You can find all of this information in Settings > About Phone. Thanks.
@userm0Wd1mRuBB, could you provide us with a little more information including model number, Baseband version, and carrier. You can find all of this information in Settings > About Phone.
If you could also include your Bixby version that would be great! You can find this information in Bixby Home > more options > Settings > About Bixby. Thanks!
I don't know if you have done this yet, but I would check your settings. Mine hasn't been working since yesterday, and I checked tonight, and the Voice Wake Up was turned off in the settings. I am not sure how that happened, but some settings ended up changed. As I said, I had no clue how that happened because it took me some digging to find the settings to turn it back on. Since it took some digging, I KNOW I didn't change it myself.