Not playing when power connected

[syproduction]

Device doesn't work at all unless i disconnect +7v (coming from DR55) from VIN on arduino.

And also i have to connect SHIELD pin from midi device to GND on Arduino. Without it it loses many messages.

[syproduction]

That was my misunderstanding of schematics of DR55 unit. We disconnected Foot switch jack to connect midi through it. Now i soldered back foot switch