Os dejo algo que han puesto e el foro de motorola, probad a ver si solución el volumen. Está en ingles
Hey guys, my notification volume is fine after last restart and do not disturb mode activated, kindly try activating the do not disturb mode for a while after restarting your phone and clear off the cache partition from the recovery mode. I'll post a step by step guide if to clear cache partition:
1) Switch off your phone
2) Press and hold power key and volume down key for 3-4 seconds, this will start your device in Fastboot Flash mode.
3) Once in that mode, guide yourself to the recovery mode through volume keys and press power key tp start your device in recovery mode.
4) The moto tag will appear and then a small android will appear with an exclamation sign saying "No command". This is recovery mode.
5) Press and hold power key, and while holding power key press volume up key and release the key while still holding the power key, you will see a display menu labelled as "Android recovery" on the top of the screen.
6) Guide yourself to wipe cache partition using volume keys and press power key when on that selection. Confirm the action of wiping cache.
7) After cache wipe is complete, reboot the system which appears as the first selection on the Android recovery screen.
8) Once the phone restarts, switch on the do not disturb mode for a while and then switch it off.
This solved the problem for me for some time, I haven't restarted my device since that cache wipe. Will post on the forum for further updates from my side.