(Trouble) Random volume drop in synths
 

Hello guys,

I'm experiencing weird and annoying things:

The main volume of my Sylenth and the patch part volume (left side) of my Virus (in Virus control plugin) drops down after a few seconds.
I take it back manually then the problem repeat itself.

No automation and no midi control influence.

I am using Ableton Live 9 on Windows 7 64 bit.

Thanks for your ideas!