I am using TIP120 transistors (controlled by 74HC595 shift registers) to control 12VDC, normally closed solenoid valves. Everything is working in short-time tests however when left overnight, some solenoids will open by themselves. I suspect a hardware issue since this occurs both when the control program is running and when it's not. Could this be an issue with the TIP120s closing their circuits after prolonged charge on the collector? Should I perhaps be using MOSFETs in this circuit instead?

Please see the full schematic and a simplified, close up schematic below.
[![simplified schematic][1]][1]

[![full schemo (pardon the mess, this was made for my own reference when making the perfboard][2]][2]


  [1]: https://i.sstatic.net/kv6nO.png
  [2]: https://i.sstatic.net/QDgYO.png