[LAU] Soundcard volume problem

Hello I've got a focusrite 18i8 usb soundcard which works fine under Fedora 25. But, from time to time, the sound levels are not correct. For example, I can have a normal level on the right channel (the one saved dugin the preceding session) and 50% on the normal level on the left channel. When I start pavucontrol, or alsamixer, all the levels seems to be correct. To fix this, the only solution I found is to start qasmixer, to switch the problematic channel to off and then to switch it back to the last value. I wanted to fill a bug report, but I don't know where to start. Is it a kernel driver problem ? Is it due to an alsa script ? Best regards, YC