There are best practices for control systems and isolation of what you are controlling.
If you turn stuff on and off and it resets Arduino you will know.
Try and generate a minimal example that reproduces the problem.
Details help to resolve issues in systems like this.
OS?
Processing version?
OSC library?
Are working over WiFi?
Using serial?
What do you observe when it hangs?
Anything in the Processing console to share?
:)