So as this is clearly a DIY setup - not using our tested components i have two guesses.
- The solenoids are the problem. The automat has ESD & self protected N Channel Smart MosFETs to drive the outputs. If they get to hot, or you make shortcut they STAY ON until you take the power away and restart without the problematic part attached. If you work with some random solenoids you need to measure the resistance of the coil and calculate the current draw. The MosFETs are rated for 1.3A continuous draw.
- If the MIDI signal gets lost on a channel / output which was on - it will stay on. The firmware isn’t counting to whatever number to shutdown the output. It’s quiet simple. If there is no Note OFF - it will stay on forever.
In your case my guess is that the solenoids are the problem. If you overdrive 5V solenoids at 24V that can be too much. Could as well be that your selfmade cables make shorts internally. It’s a guessing game. Can’t tell you more here. What is the PSU voltage?