Not sure if I found an issue with the community build, or simply finger trouble on my part, but over the last couple of days my X has twice stopped making any noise at all for ringtone, message alerts etc.
Volume is at max from the settings page, and in the ambience config (tried other ambieces too) and from the volume key.

After a reboot all returns to normal, at least for a while.

I just noticed as I missed a call from an important customer (my fault for using betas as my daily driver!), yesterday I kept noticing emails arrive without any alert sound.