Happened to me one time and it was a dodgy Erica synths mixer. The way I identified it was buy putting my modules in one by one and then turning the power on and off to see if a particular module was causing the issue.

I'm so glad I put in the extra money and bought the Intellijel’s 84 hp 7u case which gives you 3000mA on the +12v compared to arturia's 1600mA (I think), I know people rave about Arturia products but I personally have never been lucky with that company. I had power issues with a beat step pro too and when I took it apart the usb power was unsoldered from the board - really poor and cheap design choices.