I had a problem with alarms being silent in the morning when I switched to a new phone with Graphene last week.
I've read here that others have had the same or similar problem. The alarm goes off on the screen, but makes no actual sound.
I've figured out what it is. At least for me.
If I connect my phone to a Bluetooth device that supports "HD Audio" (higher bit-rate Blutooth codecs), the alarm sounds are all silent. Not even just when the alarm goes off, but while using the alarm sound selection menu also. Conveniently that makes testing easy.
As you choose alarms they normally get previewed, you get to hear each alarm sound as you select them. But they're all silent when connected to a Bluetooth HD Audio device. I tested all the codecs. While using SBC and AAC the alarm sounds work fine. Any form of AptX or LDAC and the alarms immediately go silent. Bit-rate, bit-depth, and sample-rate don't matter, simply using any higher codec kills alarm sounds.
I have no idea why this happens. I'm just glad I figured out exactly how it happens. The quickest fix for people who use a Bluetooth speaker to fall asleep to: On Bluetooth connection settings for that speaker, toggle off the HD Audio option. That should get you your alarms back.