I am wondering if I have an issue or if it is broader to everybody but since a recent update (cannot say exactly when), it seems that the volume up button function in the music apps does not respond in the watch!
I am not using it very often but for some time now (and so it has passed couple of reboots including for the watch), when I am using the 'music app' in the watch, the volume down can work but not the volume up button! And that same button is working in other apps of the watch (so not an hardware issue)
I am using the first pebble watch and the latest firmware (v3.12.2), using latest rockpool (v1.1-1), and latest sfos (2.02.51)

is it working for you?