Hello.
I am sorry you are having trouble getting your servo system to work. Since your system has trouble when multiple servos are commanded to move, but not when controlling only a few, it sounds like you might be having a power issue. If your servos are drawing more current than your power supply can handle, the voltage from the supply can drop as it tries to satisfy the current demand of the servos. If that voltage drops low enough, and you are powering your Maestro’s processor (through VIN) from the same supply, the Maestro could momentarily lose power. The Maestro might interpret this kind of brownout behavior as a serial signal error.
To correct a power issue like that, there are a few things you can try. You could use a power supply that can provide enough current for all of your servos. You could separate the servo power rails into separate power banks like Brandon describes in this post, and connect a single battery or supply to each one. For the Maestro 24-channel, you can modify the servo power rails to create up to 4 separate power banks. If you need more, you could supply power directly to your servos (be sure that your servos share a common ground with the Maestro), and/or create your own custom external power busses.
-Jon